diff --git a/e3sm_diags/derivations/derivations.py b/e3sm_diags/derivations/derivations.py
index 32b427d56..14eef3104 100644
--- a/e3sm_diags/derivations/derivations.py
+++ b/e3sm_diags/derivations/derivations.py
@@ -55,6 +55,7 @@
     pminuse_convert_units,
     precst,
     prect,
+    prect_frac,
     qflx_convert_to_lhflx,
     qflx_convert_to_lhflx_approxi,
     qflxconvert_units,
@@ -117,6 +118,16 @@
             rename(prw), target_units="kg/m2"
         ),  # EAMxx
     },
+    "PRECC": {
+        ("PRECC",): lambda pr: convert_units(pr, target_units="mm/day"),
+        ("prc",): rename,
+    },
+    "PRECL": {
+        ("PRECL",): lambda pr: convert_units(rename(pr), target_units="mm/day"),
+    },
+    "PRECC_Frac": {
+        ("PRECC", "PRECL"): lambda precc, precl: prect_frac(precc, precl),
+    },
     # Sea Surface Temperature: Degrees C
     # Temperature of the water, not the air. Ignore land.
     "SST": OrderedDict(
@@ -734,7 +745,6 @@
         ("huss",): lambda q: convert_units(q, target_units="g/kg"),
         ("d2m", "sp"): qsat,
     },
-    "PRECC": {("prc",): rename},
     "TAUX": {
         ("tauu",): lambda tauu: -tauu,
         ("surf_mom_flux_U",): lambda tauu: -tauu,  # EAMxx
diff --git a/e3sm_diags/derivations/formulas.py b/e3sm_diags/derivations/formulas.py
index 57d6e1305..e1621f965 100644
--- a/e3sm_diags/derivations/formulas.py
+++ b/e3sm_diags/derivations/formulas.py
@@ -235,6 +235,17 @@ def prect(precc: xr.DataArray, precl: xr.DataArray):
     return var
 
 
+def prect_frac(precc: xr.DataArray, precl: xr.DataArray):
+    """convective precipitation fraction = convective /(convective + large-scale)"""
+    with xr.set_options(keep_attrs=True):
+        var = precc / (precc + precl) * 100.0
+
+    var.attrs["units"] = "%"
+    var.attrs["long_name"] = "convective precipitation fraction"
+
+    return var
+
+
 def precst(precc: xr.DataArray, precl: xr.DataArray):
     """Total precipitation flux = convective + large-scale"""
     with xr.set_options(keep_attrs=True):