diff --git a/README.md b/README.md
index 77c43cf..137b8e8 100644
--- a/README.md
+++ b/README.md
@@ -178,6 +178,7 @@ We recommend you install the following CLI tools:
 | <a name="input_version_channel_group"></a> [version\_channel\_group](#input\_version\_channel\_group) | Desired channel group of the version [stable, candidate, fast, nightly]. Cannot be used together with 'channel'. Starting from RHCS Terraform provider version 1.7.7, this attribute no longer has a default value and is computed by the API. | `string` | `null` | no |
 | <a name="input_wait_for_create_complete"></a> [wait\_for\_create\_complete](#input\_wait\_for\_create\_complete) | Wait until the cluster is either in a ready state or in an error state. The waiter has a timeout of 20 minutes. (default: true) | `bool` | `true` | no |
 | <a name="input_wait_for_std_compute_nodes_complete"></a> [wait\_for\_std\_compute\_nodes\_complete](#input\_wait\_for\_std\_compute\_nodes\_complete) | Wait until the initial set of machine pools to be available. The waiter has a timeout of 60 minutes. (default: true) | `bool` | `true` | no |
+| <a name="input_worker_disk_size"></a> [worker\_disk\_size](#input\_worker\_disk\_size) | Default worker machine pool root disk size in GiB (e.g., 300, 400, 500). Leave null to use platform default. | `number` | `null` | no |
 
 ## Outputs
 
diff --git a/main.tf b/main.tf
index f6ae408..89bfb4e 100644
--- a/main.tf
+++ b/main.tf
@@ -121,6 +121,7 @@ module "rosa_cluster_hcp" {
   replicas                                  = var.replicas
   compute_machine_type                      = var.compute_machine_type
   aws_availability_zones                    = var.aws_availability_zones
+  worker_disk_size                          = var.worker_disk_size
   aws_additional_compute_security_group_ids = var.aws_additional_compute_security_group_ids
 
   ########
diff --git a/modules/rosa-cluster-hcp/README.md b/modules/rosa-cluster-hcp/README.md
index e6e703c..bc88ec6 100644
--- a/modules/rosa-cluster-hcp/README.md
+++ b/modules/rosa-cluster-hcp/README.md
@@ -124,6 +124,7 @@ No modules.
 | <a name="input_version_channel_group"></a> [version\_channel\_group](#input\_version\_channel\_group) | Desired channel group of the version [stable, candidate, fast, nightly]. Cannot be used together with 'channel'. Starting from RHCS Terraform provider version 1.7.7, this attribute no longer has a default value and is computed by the API. | `string` | `null` | no |
 | <a name="input_wait_for_create_complete"></a> [wait\_for\_create\_complete](#input\_wait\_for\_create\_complete) | Wait until the cluster is either in a ready state or in an error state. The waiter has a timeout of 20 minutes. (default: true) | `bool` | `true` | no |
 | <a name="input_wait_for_std_compute_nodes_complete"></a> [wait\_for\_std\_compute\_nodes\_complete](#input\_wait\_for\_std\_compute\_nodes\_complete) | Wait until the cluster standard compute nodes are available. The waiter has a timeout of 60 minutes. (default: true) | `bool` | `true` | no |
+| <a name="input_worker_disk_size"></a> [worker\_disk\_size](#input\_worker\_disk\_size) | Worker node root disk size in GiB. | `number` | `null` | no |
 | <a name="input_worker_role_arn"></a> [worker\_role\_arn](#input\_worker\_role\_arn) | The Amazon Resource Name (ARN) associated with the AWS IAM role that will be used by the cluster's compute instances. | `string` | `null` | no |
 
 ## Outputs
diff --git a/modules/rosa-cluster-hcp/main.tf b/modules/rosa-cluster-hcp/main.tf
index b6758be..5058774 100644
--- a/modules/rosa-cluster-hcp/main.tf
+++ b/modules/rosa-cluster-hcp/main.tf
@@ -73,6 +73,7 @@ resource "rhcs_cluster_rosa_hcp" "rosa_hcp_cluster" {
   replicas                                  = var.replicas
   aws_subnet_ids                            = var.aws_subnet_ids
   compute_machine_type                      = var.compute_machine_type
+  worker_disk_size                          = var.worker_disk_size
   create_admin_user                         = local.create_admin_user
   admin_credentials                         = local.admin_credentials
   ec2_metadata_http_tokens                  = var.ec2_metadata_http_tokens
diff --git a/modules/rosa-cluster-hcp/tests/rosa_cluster_hcp.tftest.hcl b/modules/rosa-cluster-hcp/tests/rosa_cluster_hcp.tftest.hcl
index d71d4e1..a82fde4 100644
--- a/modules/rosa-cluster-hcp/tests/rosa_cluster_hcp.tftest.hcl
+++ b/modules/rosa-cluster-hcp/tests/rosa_cluster_hcp.tftest.hcl
@@ -225,3 +225,41 @@ run "invalid_channel_three_part_version" {
     var.channel,
   ]
 }
+
+# worker_disk_size passthrough: null value (platform default).
+run "worker_disk_size_null" {
+  command = plan
+
+  providers = {
+    aws  = aws.default
+    rhcs = rhcs.import_sim
+  }
+
+  variables {
+    worker_disk_size = null
+  }
+
+  assert {
+    condition     = rhcs_cluster_rosa_hcp.rosa_hcp_cluster.worker_disk_size == null
+    error_message = "worker_disk_size must be null when set to null (platform default)."
+  }
+}
+
+# worker_disk_size passthrough: explicit value (400 GiB).
+run "worker_disk_size_explicit" {
+  command = plan
+
+  providers = {
+    aws  = aws.default
+    rhcs = rhcs.import_sim
+  }
+
+  variables {
+    worker_disk_size = 400
+  }
+
+  assert {
+    condition     = rhcs_cluster_rosa_hcp.rosa_hcp_cluster.worker_disk_size == 400
+    error_message = "worker_disk_size must be 400 when explicitly set to 400."
+  }
+}
diff --git a/modules/rosa-cluster-hcp/variables.tf b/modules/rosa-cluster-hcp/variables.tf
index 4851ae5..c8c5fc5 100644
--- a/modules/rosa-cluster-hcp/variables.tf
+++ b/modules/rosa-cluster-hcp/variables.tf
@@ -313,6 +313,20 @@ variable "aws_availability_zones" {
   description = "The AWS availability zones where instances of the default worker machine pool are deployed. Leave empty for the installer to pick availability zones"
 }
 
+variable "worker_disk_size" {
+  type        = number
+  default     = null
+  description = "Worker node root disk size in GiB."
+
+  validation {
+    condition = var.worker_disk_size == null ? true : (
+      var.worker_disk_size > 0 &&
+      floor(var.worker_disk_size) == var.worker_disk_size
+    )
+    error_message = "worker_disk_size must be a positive whole number (GiB)."
+  }
+}
+
 variable "aws_additional_compute_security_group_ids" {
   type        = list(string)
   default     = null
diff --git a/variables.tf b/variables.tf
index 9a314f2..7eba16c 100644
--- a/variables.tf
+++ b/variables.tf
@@ -247,6 +247,12 @@ variable "aws_availability_zones" {
   description = "The AWS availability zones where instances of the default worker machine pool are deployed. Leave empty for the installer to pick availability zones"
 }
 
+variable "worker_disk_size" {
+  type        = number
+  default     = null
+  description = "Default worker machine pool root disk size in GiB (e.g., 300, 400, 500). Leave null to use platform default."
+}
+
 variable "aws_additional_compute_security_group_ids" {
   type        = list(string)
   default     = null