diff --git a/pdu/pdu.go b/pdu/pdu.go
index b91f046..9a51c00 100644
--- a/pdu/pdu.go
+++ b/pdu/pdu.go
@@ -63,3 +63,6 @@ func (p *PDU_HEADER) Decode(data []uint8) error {
 	}
 	return nil
 }
+func (p *PDU_HEADER) Size() uint32 {
+	return 16
+}
\ No newline at end of file
diff --git a/pdu/pdu_test.go b/pdu/pdu_test.go
index 1e13a53..207b30f 100644
--- a/pdu/pdu_test.go
+++ b/pdu/pdu_test.go
@@ -441,3 +441,11 @@ func TestDecodeHandlesByteSlicesWithMinimumUint32Values(t *testing.T) {
 		t.Errorf("Expected command_id to be 0, got %d", p.command_id)
 	}
 }
+
+// region size
+func TestSizeReturns16(t *testing.T) {
+	var p PDU_HEADER
+	if p.Size() != 16 {
+		t.Errorf("Expected size to be 16, got %d", p.Size())
+	}
+}
\ No newline at end of file