diff --git a/crates/op-rbuilder/src/builders/flashblocks/payload.rs b/crates/op-rbuilder/src/builders/flashblocks/payload.rs
index e4bbb5cac..ff5c75f98 100644
--- a/crates/op-rbuilder/src/builders/flashblocks/payload.rs
+++ b/crates/op-rbuilder/src/builders/flashblocks/payload.rs
@@ -290,9 +290,13 @@ where
         let (payload, fb_payload) = build_block(&mut state, &ctx, &mut info)?;
 
         best_payload.set(payload.clone());
-        self.ws_pub
+        let flashblock_byte_size = self
+            .ws_pub
             .publish(&fb_payload)
             .map_err(PayloadBuilderError::other)?;
+        ctx.metrics
+            .flashblock_byte_size_histogram
+            .record(flashblock_byte_size as f64);
 
         info!(
             target: "payload_builder",
@@ -520,7 +524,8 @@ where
                                 );
                                 return Ok(());
                             }
-                            self.ws_pub
+                            let flashblock_byte_size = self
+                                .ws_pub
                                 .publish(&fb_payload)
                                 .map_err(PayloadBuilderError::other)?;
 
@@ -530,7 +535,7 @@ where
                                 .record(flashblock_build_start_time.elapsed());
                             ctx.metrics
                                 .flashblock_byte_size_histogram
-                                .record(new_payload.block().size() as f64);
+                                .record(flashblock_byte_size as f64);
                             ctx.metrics
                                 .flashblock_num_tx_histogram
                                 .record(info.executed_transactions.len() as f64);
diff --git a/crates/op-rbuilder/src/builders/flashblocks/wspub.rs b/crates/op-rbuilder/src/builders/flashblocks/wspub.rs
index 3329478be..aa34ecd7f 100644
--- a/crates/op-rbuilder/src/builders/flashblocks/wspub.rs
+++ b/crates/op-rbuilder/src/builders/flashblocks/wspub.rs
@@ -62,7 +62,7 @@ impl WebSocketPublisher {
         })
     }
 
-    pub fn publish(&self, payload: &FlashblocksPayloadV1) -> io::Result<()> {
+    pub fn publish(&self, payload: &FlashblocksPayloadV1) -> io::Result<usize> {
         // Serialize the payload to a UTF-8 string
         // serialize only once, then just copy around only a pointer
         // to the serialized data for each subscription.
@@ -76,12 +76,12 @@ impl WebSocketPublisher {
 
         let serialized = serde_json::to_string(payload)?;
         let utf8_bytes = Utf8Bytes::from(serialized);
-
+        let size = utf8_bytes.len();
         // Send the serialized payload to all subscribers
         self.pipe
             .send(utf8_bytes)
             .map_err(|e| io::Error::new(io::ErrorKind::ConnectionAborted, e))?;
-        Ok(())
+        Ok(size)
     }
 }
 
diff --git a/crates/op-rbuilder/src/metrics.rs b/crates/op-rbuilder/src/metrics.rs
index cb8aa94dc..cd0da11f7 100644
--- a/crates/op-rbuilder/src/metrics.rs
+++ b/crates/op-rbuilder/src/metrics.rs
@@ -49,7 +49,7 @@ pub struct OpRBuilderMetrics {
     pub total_block_built_gauge: Gauge,
     /// Histogram of the time taken to build a Flashblock
     pub flashblock_build_duration: Histogram,
-    /// Flashblock byte size histogram
+    /// Flashblock UTF8 payload byte size histogram
     pub flashblock_byte_size_histogram: Histogram,
     /// Histogram of transactions in a Flashblock
     pub flashblock_num_tx_histogram: Histogram,