diff --git a/crates/rundler/src/op_pool/mempool/mod.rs b/crates/rundler/src/op_pool/mempool/mod.rs
index 0d5e94960..8be005fb3 100644
--- a/crates/rundler/src/op_pool/mempool/mod.rs
+++ b/crates/rundler/src/op_pool/mempool/mod.rs
@@ -15,7 +15,7 @@ use mockall::automock;
 pub use reputation::{
     HourlyMovingAverageReputation, Reputation, ReputationParams, ReputationStatus,
 };
-use rundler_types::{Entity, EntityType, UserOperation};
+use rundler_types::{Entity, EntityType, UserOperation, USER_OPERATION_PACKED_LEN};
 use strum::IntoEnumIterator;
 use tonic::async_trait;
 
@@ -164,7 +164,7 @@ impl PoolOperation {
     }
 
     pub fn size(&self) -> usize {
-        self.uo.pack().len()
+        USER_OPERATION_PACKED_LEN
     }
 
     fn entity_address(&self, entity: EntityType) -> Option<Address> {
diff --git a/crates/types/src/lib.rs b/crates/types/src/lib.rs
index 52867fa24..268235a4e 100644
--- a/crates/types/src/lib.rs
+++ b/crates/types/src/lib.rs
@@ -8,7 +8,7 @@
 //! Rundler common types
 
 mod user_operation;
-pub use user_operation::UserOperationId;
+pub use user_operation::{UserOperationId, USER_OPERATION_PACKED_LEN};
 
 /// Generated contracts module
 #[allow(non_snake_case)]
diff --git a/crates/types/src/user_operation.rs b/crates/types/src/user_operation.rs
index 8189f58d2..92d0313c5 100644
--- a/crates/types/src/user_operation.rs
+++ b/crates/types/src/user_operation.rs
@@ -10,6 +10,9 @@ use crate::{
     UserOperation,
 };
 
+/// size of a packed user operation in bytes
+pub const USER_OPERATION_PACKED_LEN: usize = 320;
+
 /// Unique identifier for a user operation from a given sender
 #[derive(Debug, Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Hash)]
 pub struct UserOperationId {
@@ -229,4 +232,10 @@ mod tests {
                 .unwrap()
         );
     }
+
+    #[test]
+    fn test_pack_len() {
+        let user_operation = UserOperation::default();
+        assert_eq!(user_operation.pack().len(), USER_OPERATION_PACKED_LEN);
+    }
 }