diff --git a/rest-api-spec/src/yamlRestTest/resources/rest-api-spec/test/indices.delete_sample_configuration/10_basic.yml b/rest-api-spec/src/yamlRestTest/resources/rest-api-spec/test/indices.delete_sample_configuration/10_basic.yml
index a1179549546ff..4a3667b5c2e40 100644
--- a/rest-api-spec/src/yamlRestTest/resources/rest-api-spec/test/indices.delete_sample_configuration/10_basic.yml
+++ b/rest-api-spec/src/yamlRestTest/resources/rest-api-spec/test/indices.delete_sample_configuration/10_basic.yml
@@ -28,7 +28,7 @@ teardown:
         body:
           rate: 0.5
           max_samples: 100
-          max_size: "10mb"
+          max_size: "100kb"
           time_to_live: "1h"
 
   - match: { acknowledged: true }
@@ -186,7 +186,7 @@ teardown:
         body:
           rate: 0.9
           max_samples: 90
-          max_size: "20mb"
+          max_size: "100kb"
 
   - match: { acknowledged: true }
 
diff --git a/rest-api-spec/src/yamlRestTest/resources/rest-api-spec/test/indices.get_all_sample_configuration/10_basic.yml b/rest-api-spec/src/yamlRestTest/resources/rest-api-spec/test/indices.get_all_sample_configuration/10_basic.yml
index 97014cef22623..9cdfd5c371ec1 100644
--- a/rest-api-spec/src/yamlRestTest/resources/rest-api-spec/test/indices.get_all_sample_configuration/10_basic.yml
+++ b/rest-api-spec/src/yamlRestTest/resources/rest-api-spec/test/indices.get_all_sample_configuration/10_basic.yml
@@ -40,7 +40,7 @@ teardown:
         body:
           rate: 0.5
           max_samples: 100
-          max_size: "10mb"
+          max_size: "100kb"
           time_to_live: "1h"
 
   - match: { acknowledged: true }
@@ -53,7 +53,7 @@ teardown:
   - match: { configurations.0.index: "test-single-config-index" }
   - match: { configurations.0.configuration.rate: 0.5 }
   - match: { configurations.0.configuration.max_samples: 100 }
-  - match: { configurations.0.configuration.max_size: "10mb" }
+  - match: { configurations.0.configuration.max_size: "100kb" }
   - match: { configurations.0.configuration.time_to_live: "1h" }
 
 ---
@@ -85,7 +85,7 @@ teardown:
         body:
           rate: 0.7
           max_samples: 200
-          max_size: "20mb"
+          max_size: "100kb"
 
   - match: { acknowledged: true }
 
@@ -186,7 +186,7 @@ teardown:
         body:
           rate: 0.9
           max_samples: 150
-          max_size: "15mb"
+          max_size: "100kb"
 
   - match: { acknowledged: true }
 
@@ -199,7 +199,7 @@ teardown:
   - match: { configurations.0.index: "test-update-all-index" }
   - match: { configurations.0.configuration.rate: 0.9 }
   - match: { configurations.0.configuration.max_samples: 150 }
-  - match: { configurations.0.configuration.max_size: "15mb" }
+  - match: { configurations.0.configuration.max_size: "100kb" }
 
 ---
 "Get all sampling configurations after deletion":
diff --git a/rest-api-spec/src/yamlRestTest/resources/rest-api-spec/test/indices.get_sample_configuration/10_basic.yml b/rest-api-spec/src/yamlRestTest/resources/rest-api-spec/test/indices.get_sample_configuration/10_basic.yml
index 490172d78d9b0..3e5631ee718ce 100644
--- a/rest-api-spec/src/yamlRestTest/resources/rest-api-spec/test/indices.get_sample_configuration/10_basic.yml
+++ b/rest-api-spec/src/yamlRestTest/resources/rest-api-spec/test/indices.get_sample_configuration/10_basic.yml
@@ -27,7 +27,7 @@ teardown:
         body:
           rate: 0.5
           max_samples: 100
-          max_size: "10mb"
+          max_size: "100kb"
           time_to_live: "1h"
 
   - match: { acknowledged: true }
@@ -39,7 +39,7 @@ teardown:
 
   - match: { configuration.rate: 0.5 }
   - match: { configuration.max_samples: 100 }
-  - match: { configuration.max_size: "10mb" }
+  - match: { configuration.max_size: "100kb" }
   - match: { configuration.time_to_live: "1h" }
 
 ---
@@ -140,7 +140,7 @@ teardown:
         body:
           rate: 0.8
           max_samples: 75
-          max_size: "5mb"
+          max_size: "100kb"
 
   - match: { acknowledged: true }
 
@@ -152,7 +152,7 @@ teardown:
 
   - match: { configuration.rate: 0.8 }
   - match: { configuration.max_samples: 75 }
-  - match: { configuration.max_size: "5mb" }
+  - match: { configuration.max_size: "100kb" }
 
 ---
 "Get sampling configuration with master timeout":
diff --git a/rest-api-spec/src/yamlRestTest/resources/rest-api-spec/test/indices.put_sample_configuration/10_basic.yml b/rest-api-spec/src/yamlRestTest/resources/rest-api-spec/test/indices.put_sample_configuration/10_basic.yml
index b8ea5106637cb..b3324e8e637f7 100644
--- a/rest-api-spec/src/yamlRestTest/resources/rest-api-spec/test/indices.put_sample_configuration/10_basic.yml
+++ b/rest-api-spec/src/yamlRestTest/resources/rest-api-spec/test/indices.put_sample_configuration/10_basic.yml
@@ -27,7 +27,7 @@ teardown:
         body:
           rate: 0.5
           max_samples: 100
-          max_size: "10mb"
+          max_size: "100kb"
           time_to_live: "1h"
 
   - match: { acknowledged: true }
@@ -85,7 +85,7 @@ teardown:
         body:
           rate: 0.8
           max_samples: 75
-          max_size: "5mb"
+          max_size: "100kb"
 
   - match: { acknowledged: true }
 
@@ -155,7 +155,7 @@ teardown:
         body:
           rate: ".05"
           max_samples: 1000
-          max_size: "10mb"
+          max_size: "100kb"
           time_to_live: "1d"
 
   - match: { acknowledged: true }
diff --git a/server/src/internalClusterTest/java/org/elasticsearch/action/admin/indices/sampling/GetAllSampleConfigurationActionIT.java b/server/src/internalClusterTest/java/org/elasticsearch/action/admin/indices/sampling/GetAllSampleConfigurationActionIT.java
index 5cd3085e2eb60..ec0ba0a3b077c 100644
--- a/server/src/internalClusterTest/java/org/elasticsearch/action/admin/indices/sampling/GetAllSampleConfigurationActionIT.java
+++ b/server/src/internalClusterTest/java/org/elasticsearch/action/admin/indices/sampling/GetAllSampleConfigurationActionIT.java
@@ -215,7 +215,7 @@ private SamplingConfiguration randomSamplingConfiguration() {
         return new SamplingConfiguration(
             randomDoubleBetween(0.1, 1.0, true),
             randomBoolean() ? randomIntBetween(1, SamplingConfiguration.MAX_SAMPLES_LIMIT) : null,
-            randomBoolean() ? ByteSizeValue.ofGb(randomLongBetween(1, SamplingConfiguration.MAX_SIZE_LIMIT_GIGABYTES)) : null,
+            randomBoolean() ? ByteSizeValue.ofMb(randomLongBetween(1, 100)) : null,
             randomBoolean() ? randomValidTimeValue() : null,
             randomBoolean() ? randomAlphaOfLengthBetween(5, 30) : null
         );
diff --git a/server/src/main/java/org/elasticsearch/action/admin/indices/sampling/SamplingConfiguration.java b/server/src/main/java/org/elasticsearch/action/admin/indices/sampling/SamplingConfiguration.java
index 2acc016cab0be..025bc1f9e0c4e 100644
--- a/server/src/main/java/org/elasticsearch/action/admin/indices/sampling/SamplingConfiguration.java
+++ b/server/src/main/java/org/elasticsearch/action/admin/indices/sampling/SamplingConfiguration.java
@@ -15,6 +15,7 @@
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.common.unit.ByteSizeValue;
 import org.elasticsearch.core.TimeValue;
+import org.elasticsearch.monitor.jvm.JvmInfo;
 import org.elasticsearch.xcontent.ConstructingObjectParser;
 import org.elasticsearch.xcontent.ObjectParser;
 import org.elasticsearch.xcontent.ParseField;
@@ -57,10 +58,10 @@ public record SamplingConfiguration(
 
     // Constants for validation and defaults
     public static final int MAX_SAMPLES_LIMIT = 10_000;
-    public static final long MAX_SIZE_LIMIT_GIGABYTES = 5;
+    public static final double MAX_SIZE_HEAP_PERCENTAGE_LIMIT = 0.01;
+    public static final ByteSizeValue DEFAULT_MAX_SIZE_FLOOR = ByteSizeValue.ofKb(100);
     public static final long MAX_TIME_TO_LIVE_DAYS = 30;
     public static final int DEFAULT_MAX_SAMPLES = 100;
-    public static final long DEFAULT_MAX_SIZE_GIGABYTES = 1;
     public static final long DEFAULT_TIME_TO_LIVE_DAYS = 10;
 
     // Error messages
@@ -68,7 +69,11 @@ public record SamplingConfiguration(
     public static final String INVALID_MAX_SAMPLES_MIN_MESSAGE = "maxSamples must be greater than 0";
     public static final String INVALID_MAX_SAMPLES_MAX_MESSAGE = "maxSamples must be less than or equal to " + MAX_SAMPLES_LIMIT;
     public static final String INVALID_MAX_SIZE_MIN_MESSAGE = "maxSize must be greater than 0";
-    public static final String INVALID_MAX_SIZE_MAX_MESSAGE = "maxSize must be less than or equal to " + MAX_SIZE_LIMIT_GIGABYTES + "GB";
+    public static final String INVALID_MAX_SIZE_MAX_MESSAGE = "maxSize must be less than or equal to "
+        + (int) (MAX_SIZE_HEAP_PERCENTAGE_LIMIT * 100)
+        + "% of heap size ("
+        + calculateDefaultMaxSize().toString()
+        + ")";
     public static final String INVALID_TIME_TO_LIVE_MIN_MESSAGE = "timeToLive must be greater than 0";
     public static final String INVALID_TIME_TO_LIVE_MAX_MESSAGE = "timeToLive must be less than or equal to "
         + MAX_TIME_TO_LIVE_DAYS
@@ -152,7 +157,7 @@ public record SamplingConfiguration(
      *
      * @param rate The fraction of documents to sample (must be between 0 and 1)
      * @param maxSamples The maximum number of documents to sample (optional, defaults to {@link #DEFAULT_MAX_SAMPLES})
-     * @param maxSize The maximum total size of sampled documents (optional, defaults to {@link #DEFAULT_MAX_SIZE_GIGABYTES} GB)
+     * @param maxSize The maximum total size of sampled documents (optional, defaults to {@link #MAX_SIZE_HEAP_PERCENTAGE_LIMIT} of heap)
      * @param timeToLive The duration for which the sampled documents
      *                   should be retained (optional, defaults to {@link #DEFAULT_TIME_TO_LIVE_DAYS} days)
      * @param condition An optional condition script that sampled documents must satisfy (optional, can be null)
@@ -168,12 +173,23 @@ public SamplingConfiguration(
     ) {
         this.rate = rate;
         this.maxSamples = maxSamples == null ? DEFAULT_MAX_SAMPLES : maxSamples;
-        this.maxSize = maxSize == null ? ByteSizeValue.ofGb(DEFAULT_MAX_SIZE_GIGABYTES) : maxSize;
+        this.maxSize = maxSize == null ? calculateDefaultMaxSize() : maxSize;
         this.timeToLive = timeToLive == null ? TimeValue.timeValueDays(DEFAULT_TIME_TO_LIVE_DAYS) : timeToLive;
         this.condition = condition;
         this.creationTime = creationTime == null ? Instant.now().toEpochMilli() : creationTime;
     }
 
+    /**
+     * Calculates the default max size as a percentage of the configured heap size,
+     * with a minimum floor value.
+     *
+     * @return The default max size value
+     */
+    private static ByteSizeValue calculateDefaultMaxSize() {
+        long heapBasedSize = (long) (MAX_SIZE_HEAP_PERCENTAGE_LIMIT * JvmInfo.jvmInfo().getConfiguredMaxHeapSize());
+        return ByteSizeValue.ofBytes(Math.max(heapBasedSize, DEFAULT_MAX_SIZE_FLOOR.getBytes()));
+    }
+
     // Convenience constructor without creationTime
     public SamplingConfiguration(double rate, Integer maxSamples, ByteSizeValue maxSize, TimeValue timeToLive, String condition) {
         this(rate, maxSamples, maxSize, timeToLive, condition, null);
@@ -266,7 +282,7 @@ private static void validateInputs(double rate, Integer maxSamples, ByteSizeValu
             if (maxSize.compareTo(ByteSizeValue.ZERO) <= 0) {
                 throw new IllegalArgumentException(INVALID_MAX_SIZE_MIN_MESSAGE);
             }
-            ByteSizeValue maxLimit = ByteSizeValue.ofGb(MAX_SIZE_LIMIT_GIGABYTES);
+            ByteSizeValue maxLimit = calculateDefaultMaxSize();
             if (maxSize.compareTo(maxLimit) > 0) {
                 throw new IllegalArgumentException(INVALID_MAX_SIZE_MAX_MESSAGE);
             }
diff --git a/server/src/test/java/org/elasticsearch/action/admin/indices/sampling/GetAllSampleConfigurationActionResponseTests.java b/server/src/test/java/org/elasticsearch/action/admin/indices/sampling/GetAllSampleConfigurationActionResponseTests.java
index ce93824c6b6c7..0e11ad1c0123c 100644
--- a/server/src/test/java/org/elasticsearch/action/admin/indices/sampling/GetAllSampleConfigurationActionResponseTests.java
+++ b/server/src/test/java/org/elasticsearch/action/admin/indices/sampling/GetAllSampleConfigurationActionResponseTests.java
@@ -81,7 +81,7 @@ private SamplingConfiguration createRandomSamplingConfiguration() {
         return new SamplingConfiguration(
             randomDoubleBetween(0.1, 1.0, true),
             randomBoolean() ? randomIntBetween(1, 1000) : null,
-            randomBoolean() ? ByteSizeValue.ofMb(randomIntBetween(1, 100)) : null,
+            randomBoolean() ? null : ByteSizeValue.ofKb(randomIntBetween(50, 100)),
             randomBoolean() ? TimeValue.timeValueMinutes(randomIntBetween(1, 60)) : null,
             randomBoolean() ? "ctx?.field == 'test'" : null
         );
diff --git a/server/src/test/java/org/elasticsearch/action/admin/indices/sampling/GetSampleConfigurationActionResponseTests.java b/server/src/test/java/org/elasticsearch/action/admin/indices/sampling/GetSampleConfigurationActionResponseTests.java
index 0455458af07c2..398cc60c0b3da 100644
--- a/server/src/test/java/org/elasticsearch/action/admin/indices/sampling/GetSampleConfigurationActionResponseTests.java
+++ b/server/src/test/java/org/elasticsearch/action/admin/indices/sampling/GetSampleConfigurationActionResponseTests.java
@@ -47,7 +47,7 @@ private SamplingConfiguration createRandomSamplingConfiguration() {
         return new SamplingConfiguration(
             randomDoubleBetween(0.1, 1.0, true),
             randomBoolean() ? randomIntBetween(1, 1000) : null,
-            randomBoolean() ? ByteSizeValue.ofMb(randomIntBetween(1, 100)) : null,
+            randomBoolean() ? null : ByteSizeValue.ofKb(randomIntBetween(50, 100)),
             randomBoolean() ? TimeValue.timeValueMinutes(randomIntBetween(1, 60)) : null,
             randomBoolean() ? "ctx?.field == 'test'" : null
         );
diff --git a/server/src/test/java/org/elasticsearch/action/admin/indices/sampling/PutSampleConfigurationActionTests.java b/server/src/test/java/org/elasticsearch/action/admin/indices/sampling/PutSampleConfigurationActionTests.java
index a4fc1b91e491c..eb0b8b99d8975 100644
--- a/server/src/test/java/org/elasticsearch/action/admin/indices/sampling/PutSampleConfigurationActionTests.java
+++ b/server/src/test/java/org/elasticsearch/action/admin/indices/sampling/PutSampleConfigurationActionTests.java
@@ -114,7 +114,7 @@ private static SamplingConfiguration createRandomSampleConfig() {
         return new SamplingConfiguration(
             randomDoubleBetween(0.0, 1.0, true),
             randomBoolean() ? null : randomIntBetween(1, 1000),
-            randomBoolean() ? null : ByteSizeValue.ofGb(randomIntBetween(1, 5)),
+            randomBoolean() ? null : ByteSizeValue.ofKb(randomIntBetween(50, 100)),
             randomBoolean() ? null : new TimeValue(randomIntBetween(1, 30), TimeUnit.DAYS),
             randomBoolean() ? randomAlphaOfLength(10) : null
         );
diff --git a/server/src/test/java/org/elasticsearch/action/admin/indices/sampling/SamplingConfigurationTests.java b/server/src/test/java/org/elasticsearch/action/admin/indices/sampling/SamplingConfigurationTests.java
index f1be044f1c453..b9c404bb86b12 100644
--- a/server/src/test/java/org/elasticsearch/action/admin/indices/sampling/SamplingConfigurationTests.java
+++ b/server/src/test/java/org/elasticsearch/action/admin/indices/sampling/SamplingConfigurationTests.java
@@ -11,6 +11,7 @@
 import org.elasticsearch.common.io.stream.Writeable;
 import org.elasticsearch.common.unit.ByteSizeValue;
 import org.elasticsearch.core.TimeValue;
+import org.elasticsearch.monitor.jvm.JvmInfo;
 import org.elasticsearch.test.AbstractXContentSerializingTestCase;
 import org.elasticsearch.xcontent.ToXContent;
 import org.elasticsearch.xcontent.XContentParser;
@@ -40,10 +41,12 @@ protected Writeable.Reader<SamplingConfiguration> instanceReader() {
 
     @Override
     protected SamplingConfiguration createTestInstance() {
+        long maxHeap = JvmInfo.jvmInfo().getConfiguredMaxHeapSize();
+        long maxSizeLimit = (long) (SamplingConfiguration.MAX_SIZE_HEAP_PERCENTAGE_LIMIT * maxHeap);
         return new SamplingConfiguration(
             randomDoubleBetween(0.0, 1.0, true),
             randomBoolean() ? null : randomIntBetween(1, SamplingConfiguration.MAX_SAMPLES_LIMIT),
-            randomBoolean() ? null : ByteSizeValue.ofGb(randomLongBetween(1, SamplingConfiguration.MAX_SIZE_LIMIT_GIGABYTES)),
+            randomBoolean() ? null : ByteSizeValue.ofBytes(randomLongBetween(1, maxSizeLimit)),
             randomBoolean() ? null : TimeValue.timeValueDays(randomLongBetween(1, SamplingConfiguration.MAX_TIME_TO_LIVE_DAYS)),
             randomBoolean() ? null : randomAlphaOfLength(10)
         );
@@ -51,6 +54,8 @@ protected SamplingConfiguration createTestInstance() {
 
     @Override
     protected SamplingConfiguration mutateInstance(SamplingConfiguration instance) {
+        long maxHeap = JvmInfo.jvmInfo().getConfiguredMaxHeapSize();
+        long maxSizeLimit = (long) (SamplingConfiguration.MAX_SIZE_HEAP_PERCENTAGE_LIMIT * maxHeap);
         return switch (randomIntBetween(0, 4)) {
             case 0 -> new SamplingConfiguration(
                 randomValueOtherThan(instance.rate(), () -> randomDoubleBetween(0.0, 1.0, true)),
@@ -69,10 +74,7 @@ protected SamplingConfiguration mutateInstance(SamplingConfiguration instance) {
             case 2 -> new SamplingConfiguration(
                 instance.rate(),
                 instance.maxSamples(),
-                randomValueOtherThan(
-                    instance.maxSize(),
-                    () -> ByteSizeValue.ofGb(randomLongBetween(1, SamplingConfiguration.MAX_SIZE_LIMIT_GIGABYTES))
-                ),
+                randomValueOtherThan(instance.maxSize(), () -> ByteSizeValue.ofBytes(randomLongBetween(1, maxSizeLimit))),
                 instance.timeToLive(),
                 instance.condition()
             );
@@ -101,7 +103,11 @@ public void testDefaults() {
         SamplingConfiguration config = new SamplingConfiguration(0.5, null, null, null, null);
         assertThat(config.rate(), equalTo(0.5));
         assertThat(config.maxSamples(), equalTo(SamplingConfiguration.DEFAULT_MAX_SAMPLES));
-        assertThat(config.maxSize(), equalTo(ByteSizeValue.ofGb(SamplingConfiguration.DEFAULT_MAX_SIZE_GIGABYTES)));
+        long expectedDefaultMaxSize = Math.max(
+            (long) (SamplingConfiguration.MAX_SIZE_HEAP_PERCENTAGE_LIMIT * JvmInfo.jvmInfo().getConfiguredMaxHeapSize()),
+            SamplingConfiguration.DEFAULT_MAX_SIZE_FLOOR.getBytes()
+        );
+        assertThat(config.maxSize(), equalTo(ByteSizeValue.ofBytes(expectedDefaultMaxSize)));
         assertThat(config.timeToLive(), equalTo(TimeValue.timeValueDays(SamplingConfiguration.DEFAULT_TIME_TO_LIVE_DAYS)));
         assertThat(config.condition(), nullValue());
     }
@@ -157,12 +163,15 @@ public void testValidation() throws IOException {
             }
             """, SamplingConfiguration.INVALID_MAX_SIZE_MIN_MESSAGE);
 
+        // Test max size exceeding heap-based limit
+        long maxHeap = JvmInfo.jvmInfo().getConfiguredMaxHeapSize();
+        long maxSizeLimit = (long) (SamplingConfiguration.MAX_SIZE_HEAP_PERCENTAGE_LIMIT * maxHeap);
         assertValidationError(String.format(Locale.ROOT, """
             {
               "rate": 0.5,
-              "max_size": "%dgb"
+              "max_size_in_bytes": %d
             }
-            """, SamplingConfiguration.MAX_SIZE_LIMIT_GIGABYTES + 1), SamplingConfiguration.INVALID_MAX_SIZE_MAX_MESSAGE);
+            """, maxSizeLimit + 1), SamplingConfiguration.INVALID_MAX_SIZE_MAX_MESSAGE);
 
         // Test invalid timeToLive
         assertValidationError("""
@@ -234,24 +243,17 @@ public void testValidInputs() throws IOException {
         assertThat(config.maxSamples(), equalTo(1));
 
         // Test boundary conditions - maximum values
-        parser = createParser(
-            JsonXContent.jsonXContent,
-            String.format(
-                Locale.ROOT,
-                """
-                    {
-                      "rate": 1.0,
-                      "max_samples": %d,
-                      "max_size": "%dgb",
-                      "time_to_live": "%dd",
-                      "if": "test_condition"
-                    }
-                    """,
-                SamplingConfiguration.MAX_SAMPLES_LIMIT,
-                SamplingConfiguration.MAX_SIZE_LIMIT_GIGABYTES,
-                SamplingConfiguration.MAX_TIME_TO_LIVE_DAYS
-            )
-        );
+        long maxHeap = JvmInfo.jvmInfo().getConfiguredMaxHeapSize();
+        long maxSizeLimit = (long) (SamplingConfiguration.MAX_SIZE_HEAP_PERCENTAGE_LIMIT * maxHeap);
+        parser = createParser(JsonXContent.jsonXContent, String.format(Locale.ROOT, """
+            {
+              "rate": 1.0,
+              "max_samples": %d,
+              "max_size_in_bytes": %d,
+              "time_to_live": "%dd",
+              "if": "test_condition"
+            }
+            """, SamplingConfiguration.MAX_SAMPLES_LIMIT, maxSizeLimit, SamplingConfiguration.MAX_TIME_TO_LIVE_DAYS));
         config = SamplingConfiguration.fromXContent(parser);
         assertThat(config.rate(), equalTo(1.0));
         assertThat(config.maxSamples(), equalTo(SamplingConfiguration.MAX_SAMPLES_LIMIT));
@@ -332,4 +334,20 @@ public void testCreationTimeUserDataRestrictionRaw() throws IOException {
         assertNotNull("Expected IllegalArgumentException with creation_time_in_millis message", cause);
         assertThat(cause.getMessage(), equalTo("Creation time cannot be set by user (field: creation_time_in_millis)"));
     }
+
+    public void testMinimumDefaultMaxSize() {
+        // Test that the minimum default max size is enforced
+        SamplingConfiguration config = new SamplingConfiguration(0.5, null, null, null, null);
+
+        // Calculate what the heap percentage would give us
+        long heapBasedSize = (long) (SamplingConfiguration.MAX_SIZE_HEAP_PERCENTAGE_LIMIT * JvmInfo.jvmInfo().getConfiguredMaxHeapSize());
+        long minSize = SamplingConfiguration.DEFAULT_MAX_SIZE_FLOOR.getBytes();
+
+        // The actual default should be the larger of the two
+        long expectedSize = Math.max(heapBasedSize, minSize);
+        assertThat(config.maxSize().getBytes(), equalTo(expectedSize));
+
+        // Verify it's at least the minimum
+        assertThat(config.maxSize().getBytes(), greaterThanOrEqualTo(minSize));
+    }
 }
diff --git a/server/src/test/java/org/elasticsearch/action/admin/indices/sampling/SamplingMetadataTests.java b/server/src/test/java/org/elasticsearch/action/admin/indices/sampling/SamplingMetadataTests.java
index bbccbe315051c..cc49020a00cb2 100644
--- a/server/src/test/java/org/elasticsearch/action/admin/indices/sampling/SamplingMetadataTests.java
+++ b/server/src/test/java/org/elasticsearch/action/admin/indices/sampling/SamplingMetadataTests.java
@@ -94,7 +94,7 @@ private static SamplingConfiguration createRandomSampleConfig() {
         return new SamplingConfiguration(
             randomDoubleBetween(0.0, 1.0, true),
             randomBoolean() ? null : randomIntBetween(1, 1000),
-            randomBoolean() ? null : ByteSizeValue.ofGb(randomIntBetween(1, 5)),
+            randomBoolean() ? null : ByteSizeValue.ofKb(randomIntBetween(50, 100)),
             randomBoolean() ? null : new TimeValue(randomIntBetween(1, 30), TimeUnit.DAYS),
             randomBoolean() ? randomAlphaOfLength(10) : null
         );
diff --git a/server/src/test/java/org/elasticsearch/action/admin/indices/sampling/TransportDeleteSampleConfigurationActionTests.java b/server/src/test/java/org/elasticsearch/action/admin/indices/sampling/TransportDeleteSampleConfigurationActionTests.java
index f18d59b2e241f..75d00b2606d3f 100644
--- a/server/src/test/java/org/elasticsearch/action/admin/indices/sampling/TransportDeleteSampleConfigurationActionTests.java
+++ b/server/src/test/java/org/elasticsearch/action/admin/indices/sampling/TransportDeleteSampleConfigurationActionTests.java
@@ -352,7 +352,7 @@ private SamplingConfiguration createRandomSamplingConfiguration() {
         return new SamplingConfiguration(
             randomDoubleBetween(0.0, 1.0, true),
             randomBoolean() ? null : randomIntBetween(1, SamplingConfiguration.MAX_SAMPLES_LIMIT),
-            randomBoolean() ? null : ByteSizeValue.ofGb(randomLongBetween(1, SamplingConfiguration.MAX_SIZE_LIMIT_GIGABYTES)),
+            randomBoolean() ? null : ByteSizeValue.ofMb(randomLongBetween(1, 100)),
             randomBoolean() ? null : TimeValue.timeValueDays(randomLongBetween(1, SamplingConfiguration.MAX_TIME_TO_LIVE_DAYS)),
             randomBoolean() ? null : randomAlphaOfLength(10)
         );
diff --git a/server/src/test/java/org/elasticsearch/action/admin/indices/sampling/TransportPutSampleConfigurationActionTests.java b/server/src/test/java/org/elasticsearch/action/admin/indices/sampling/TransportPutSampleConfigurationActionTests.java
index b71ce2ff3f1d5..fdab82d49c00a 100644
--- a/server/src/test/java/org/elasticsearch/action/admin/indices/sampling/TransportPutSampleConfigurationActionTests.java
+++ b/server/src/test/java/org/elasticsearch/action/admin/indices/sampling/TransportPutSampleConfigurationActionTests.java
@@ -205,7 +205,7 @@ private SamplingConfiguration createRandomSamplingConfiguration() {
         return new SamplingConfiguration(
             randomDoubleBetween(0.0, 1.0, true),
             randomBoolean() ? null : randomIntBetween(1, SamplingConfiguration.MAX_SAMPLES_LIMIT),
-            randomBoolean() ? null : ByteSizeValue.ofGb(randomLongBetween(1, SamplingConfiguration.MAX_SIZE_LIMIT_GIGABYTES)),
+            randomBoolean() ? null : ByteSizeValue.ofMb(randomLongBetween(1, 100)),
             randomBoolean() ? null : TimeValue.timeValueDays(randomLongBetween(1, SamplingConfiguration.MAX_TIME_TO_LIVE_DAYS)),
             randomBoolean() ? null : randomAlphaOfLength(10)
         );
diff --git a/server/src/test/java/org/elasticsearch/ingest/SamplingServiceTests.java b/server/src/test/java/org/elasticsearch/ingest/SamplingServiceTests.java
index 1b812a446365b..d67acd8e7a262 100644
--- a/server/src/test/java/org/elasticsearch/ingest/SamplingServiceTests.java
+++ b/server/src/test/java/org/elasticsearch/ingest/SamplingServiceTests.java
@@ -71,7 +71,7 @@ public void testMaybeSample() {
             .putCustom(
                 SamplingMetadata.TYPE,
                 new SamplingMetadata(
-                    Map.of(indexName, new SamplingConfiguration(1.0, maxSize, ByteSizeValue.ofMb(100), TimeValue.timeValueDays(3), null))
+                    Map.of(indexName, new SamplingConfiguration(1.0, maxSize, ByteSizeValue.ofKb(100), TimeValue.timeValueDays(3), null))
                 )
             );
         projectMetadata = projectBuilder.build();
@@ -138,7 +138,7 @@ public void testMaybeSampleWithCondition() {
                 new SamplingMetadata(
                     Map.of(
                         indexName,
-                        new SamplingConfiguration(1.0, 100, ByteSizeValue.ofMb(100), TimeValue.timeValueDays(3), TEST_CONDITIONAL_SCRIPT)
+                        new SamplingConfiguration(1.0, 100, ByteSizeValue.ofMb(5), TimeValue.timeValueDays(3), TEST_CONDITIONAL_SCRIPT)
                     )
                 )
             );
@@ -183,7 +183,7 @@ public void testMaybeSampleWithLowRate() {
             .putCustom(
                 SamplingMetadata.TYPE,
                 new SamplingMetadata(
-                    Map.of(indexName, new SamplingConfiguration(0.001, 100, ByteSizeValue.ofMb(100), TimeValue.timeValueDays(3), null))
+                    Map.of(indexName, new SamplingConfiguration(0.001, 100, ByteSizeValue.ofMb(5), TimeValue.timeValueDays(3), null))
                 )
             );
         final ProjectId projectId = projectBuilder.getId();
@@ -223,7 +223,7 @@ public void testMaybeSampleMaxSamples() {
             .putCustom(
                 SamplingMetadata.TYPE,
                 new SamplingMetadata(
-                    Map.of(indexName, new SamplingConfiguration(1.0, maxSamples, ByteSizeValue.ofMb(100), TimeValue.timeValueDays(3), null))
+                    Map.of(indexName, new SamplingConfiguration(1.0, maxSamples, ByteSizeValue.ofMb(5), TimeValue.timeValueDays(3), null))
                 )
             );
         final ProjectId projectId = projectBuilder.getId();
diff --git a/server/src/test/java/org/elasticsearch/ingest/UpdateSamplingConfigurationExecutorTests.java b/server/src/test/java/org/elasticsearch/ingest/UpdateSamplingConfigurationExecutorTests.java
index 68401dd54eb96..470cf24b41de3 100644
--- a/server/src/test/java/org/elasticsearch/ingest/UpdateSamplingConfigurationExecutorTests.java
+++ b/server/src/test/java/org/elasticsearch/ingest/UpdateSamplingConfigurationExecutorTests.java
@@ -83,7 +83,7 @@ public void testExecuteTaskWithUpperBoundLimit() {
         SamplingConfiguration defaultConfig = new SamplingConfiguration(
             0.5d,
             50,
-            ByteSizeValue.ofMb(10),
+            ByteSizeValue.ofKb(100),
             TimeValue.timeValueHours(1),
             null
         );
@@ -106,7 +106,7 @@ public void testExecuteTaskWithUpperBoundLimit() {
 
         // Try to add the 101st configuration - this should fail
         String newIndexName = "new-index-101";
-        SamplingConfiguration newConfig = new SamplingConfiguration(0.8d, 80, ByteSizeValue.ofMb(20), TimeValue.timeValueHours(2), null);
+        SamplingConfiguration newConfig = new SamplingConfiguration(0.8d, 80, ByteSizeValue.ofKb(100), TimeValue.timeValueHours(2), null);
 
         SamplingService.UpdateSamplingConfigurationTask task = new SamplingService.UpdateSamplingConfigurationTask(
             ProjectId.DEFAULT,