diff --git a/modules/project-factory/README.md b/modules/project-factory/README.md
index b19b98453..6faa885aa 100644
--- a/modules/project-factory/README.md
+++ b/modules/project-factory/README.md
@@ -214,16 +214,19 @@ The following table lists the available context interpolations. External context
 |                     |                      |                     | IaC service accounts               |
 |                     |                      |                     | other project service accounts     |
 |                     |                      |                     | other project IaC service accounts |
+|                     |                      |                     | project number in principals |
 | project             | tag bindings         | `tag_values`        |                                    |
 | project             | IAM principals       | `iam_principals`    | project service accounts           |
 |                     |                      |                     | IaC service accounts               |
 |                     |                      |                     | other project service accounts     |
 |                     |                      |                     | other project service agents     |
 |                     |                      |                     | other project IaC service accounts |
+|                     |                      |                     | project number in principals |
 | bucket              | IAM principals       | `iam_principals`    | project service accounts           |
 |                     |                      |                     | IaC service accounts               |
 |                     |                      |                     | other project service accounts     |
 |                     |                      |                     | other project IaC service accounts |
+|                     |                      |                     | project number in principals |
 | service account     | IAM projects         | `vpc_host_projects` |                                    |
 | service account     | `iam_sa_roles` |                     | service accounts in the same project |
 | IaC bucket          | IAM principals       | `iam_principals`    | IaC service accounts               |
diff --git a/modules/project-factory/main.tf b/modules/project-factory/main.tf
index 8976bdb2b..71022959e 100644
--- a/modules/project-factory/main.tf
+++ b/modules/project-factory/main.tf
@@ -155,7 +155,9 @@ module "projects-iam" {
         # passthrough + error handling using tonumber until Terraform gets fail/raise function
         (
           strcontains(vv, ":")
-          ? vv
+          ? templatestring(
+            vv, { project_number = module.projects[each.key].number }
+          )
           : tonumber("[Error] Invalid member: '${vv}' in project '${each.key}'")
         )
       )
@@ -180,7 +182,9 @@ module "projects-iam" {
           # passthrough + error handling using tonumber until Terraform gets fail/raise function
           (
             strcontains(vv, ":")
-            ? vv
+            ? templatestring(
+              vv, { project_number = module.projects[each.key].number }
+            )
             : tonumber("[Error] Invalid member: '${vv}' in project '${each.key}'")
           )
         )
@@ -206,7 +210,9 @@ module "projects-iam" {
         # passthrough + error handling using tonumber until Terraform gets fail/raise function
         (
           strcontains(v.member, ":")
-          ? v.member
+          ? templatestring(
+            v.member, { project_number = module.projects[each.key].number }
+          )
           : tonumber("[Error] Invalid member: '${v.member}' in project '${each.key}'")
         )
       )
@@ -231,7 +237,9 @@ module "projects-iam" {
       # passthrough + error handling using tonumber until Terraform gets fail/raise function
       (
         strcontains(k, ":")
-        ? k
+        ? templatestring(
+          k, { project_number = module.projects[each.key].number }
+        )
         : tonumber("[Error] Invalid member: '${k}' in project '${each.key}'")
       )
       ) => [
@@ -267,7 +275,9 @@ module "projects-iam" {
             # passthrough + error handling using tonumber until Terraform gets fail/raise function
             (
               strcontains(v.member, ":")
-              ? v.member
+              ? templatestring(
+                v.member, { project_number = module.projects[each.key].number }
+              )
               : tonumber("[Error] Invalid member: '${v.member}' in project '${each.key}'")
             )
           )
@@ -290,7 +300,9 @@ module "projects-iam" {
           # passthrough + error handling using tonumber until Terraform gets fail/raise function
           (
             strcontains(vv, ":")
-            ? vv
+            ? templatestring(
+              vv, { project_number = module.projects[each.key].number }
+            )
             : tonumber("[Error] Invalid member: '${vv}' in project '${each.key}'")
           )
         )
@@ -329,7 +341,9 @@ module "buckets" {
         # passthrough + error handling using tonumber until Terraform gets fail/raise function
         (
           strcontains(vv, ":")
-          ? vv
+          ? templatestring(
+            vv, { project_number = module.projects[each.key].number }
+          )
           : tonumber("[Error] Invalid member: '${vv}' in project '${each.value.project_key}'")
         )
       )
@@ -352,7 +366,9 @@ module "buckets" {
           # passthrough + error handling using tonumber until Terraform gets fail/raise function
           (
             strcontains(vv, ":")
-            ? vv
+            ? templatestring(
+              vv, { project_number = module.projects[each.key].number }
+            )
             : tonumber("[Error] Invalid member: '${vv}' in project '${each.value.project}'")
           )
         )
@@ -375,7 +391,9 @@ module "buckets" {
         # passthrough + error handling using tonumber until Terraform gets fail/raise function
         (
           strcontains(v.member, ":")
-          ? v.member
+          ? templatestring(
+            v.member, { project_number = module.projects[each.key].number }
+          )
           : tonumber("[Error] Invalid member: '${v.member}' in project '${each.value.project}'")
         )
       )