diff --git a/esphome/components/api/api_connection.cpp b/esphome/components/api/api_connection.cpp
index 0d3b99cd41..e21fcb694a 100644
--- a/esphome/components/api/api_connection.cpp
+++ b/esphome/components/api/api_connection.cpp
@@ -290,8 +290,9 @@ uint16_t APIConnection::encode_message_to_buffer(ProtoMessage &msg, uint8_t mess
 #endif
 
   // Calculate size
-  uint32_t calculated_size = 0;
-  msg.calculate_size(calculated_size);
+  ProtoSize size_calc;
+  msg.calculate_size(size_calc);
+  uint32_t calculated_size = size_calc.get_size();
 
   // Cache frame sizes to avoid repeated virtual calls
   const uint8_t header_padding = conn->helper_->frame_header_padding();