diff --git a/chronik/chronik-bridge/src/ffi.rs b/chronik/chronik-bridge/src/ffi.rs
--- a/chronik/chronik-bridge/src/ffi.rs
+++ b/chronik/chronik-bridge/src/ffi.rs
@@ -52,6 +52,8 @@
         pub data_pos: u32,
         /// Position of the undo data within the undo file.
         pub undo_pos: u32,
+        /// Serialized size of the block
+        pub size: u64,
         /// Txs of this block, including positions within the block/undo files.
         pub txs: Vec<BlockTx>,
     }
diff --git a/chronik/chronik-cpp/chronik_bridge.cpp b/chronik/chronik-cpp/chronik_bridge.cpp
--- a/chronik/chronik-cpp/chronik_bridge.cpp
+++ b/chronik/chronik-cpp/chronik_bridge.cpp
@@ -149,6 +149,7 @@
             .file_num = uint32_t(bindex.nFile),
             .data_pos = bindex.nDataPos,
             .undo_pos = bindex.nUndoPos,
+            .size = bindex.nSize,
             .txs = bridged_txs};
 }
 
diff --git a/chronik/test/bridgeprimitives_tests.cpp b/chronik/test/bridgeprimitives_tests.cpp
--- a/chronik/test/bridgeprimitives_tests.cpp
+++ b/chronik/test/bridgeprimitives_tests.cpp
@@ -64,6 +64,7 @@
     BOOST_CHECK_EQUAL(left.file_num, right.file_num);
     BOOST_CHECK_EQUAL(left.data_pos, right.data_pos);
     BOOST_CHECK_EQUAL(left.undo_pos, right.undo_pos);
+    BOOST_CHECK_EQUAL(left.size, right.size);
 
     BOOST_CHECK_EQUAL(left.txs.size(), right.txs.size());
     for (size_t txIdx = 0; txIdx < left.txs.size(); ++txIdx) {
@@ -144,6 +145,7 @@
         .file_num = 0,
         .data_pos = 8, // 8 magic bytes in block file
         .undo_pos = 0, // genesis has no undo data
+        .size = 285,
         .txs = {{
             .tx = expectedGenesisTx,
             .data_pos = 89, // +80 header +1 compact size
@@ -296,6 +298,7 @@
         .file_num = 0,
         .data_pos = 39948,
         .undo_pos = 8249,
+        .size = 578,
         .txs = {
             {.tx = expectedTestTx0, .data_pos = 40029, .undo_pos = 0},
             {.tx = expectedTestTx1, .data_pos = 40129, .undo_pos = 8250},