diff --git a/esphome/components/api/api_pb2.cpp b/esphome/components/api/api_pb2.cpp
index 058a722483..1c7012370b 100644
--- a/esphome/components/api/api_pb2.cpp
+++ b/esphome/components/api/api_pb2.cpp
@@ -1149,7 +1149,7 @@ void ExecuteServiceResponse::calculate_size(ProtoSize &size) const {
   size.add_bool(1, this->success);
   size.add_length(1, this->error_message_ref_.size());
 #ifdef USE_API_USER_DEFINED_ACTION_RESPONSES_JSON
-  size.add_length(4, this->response_data_len);
+  size.add_length(1, this->response_data_len);
 #endif
 }
 #endif
@@ -3399,7 +3399,7 @@ void ZWaveProxyRequest::encode(ProtoWriteBuffer buffer) const {
 }
 void ZWaveProxyRequest::calculate_size(ProtoSize &size) const {
   size.add_uint32(1, static_cast<uint32_t>(this->type));
-  size.add_length(2, this->data_len);
+  size.add_length(1, this->data_len);
 }
 #endif
 
diff --git a/script/api_protobuf/api_protobuf.py b/script/api_protobuf/api_protobuf.py
index 89f9ecaf4a..af7d6af954 100755
--- a/script/api_protobuf/api_protobuf.py
+++ b/script/api_protobuf/api_protobuf.py
@@ -907,7 +907,7 @@ class PointerToBytesBufferType(PointerToBufferTypeBase):
         )
 
     def get_size_calculation(self, name: str, force: bool = False) -> str:
-        return f"size.add_length({self.number}, this->{self.field_name}_len);"
+        return f"size.add_length({self.calculate_field_id_size()}, this->{self.field_name}_len);"
 
 
 class PointerToStringBufferType(PointerToBufferTypeBase):
@@ -932,7 +932,6 @@ class PointerToStringBufferType(PointerToBufferTypeBase):
     @property
     def decode_length_content(self) -> str | None:
         return f"""case {self.number}: {{
-      // Use raw data directly via StringRef to avoid allocation
       this->{self.field_name} = StringRef(reinterpret_cast<const char *>(value.data()), value.size());
       break;
     }}"""