diff --git a/esphome/components/api/api_pb2.cpp b/esphome/components/api/api_pb2.cpp
index e2b9dd7b70..66623c0ab0 100644
--- a/esphome/components/api/api_pb2.cpp
+++ b/esphome/components/api/api_pb2.cpp
@@ -512,9 +512,7 @@ uint32_t ListEntitiesLightResponse::calculate_size() const {
   size += 5;
   size += ProtoSize::calc_length(1, this->name.size());
   if (!this->supported_color_modes->empty()) {
-    for (const auto &it : *this->supported_color_modes) {
-      size += 2;
-    }
+    size += this->supported_color_modes->size() * 2;
   }
   size += ProtoSize::calc_float(1, this->min_mireds);
   size += ProtoSize::calc_float(1, this->max_mireds);
@@ -1379,23 +1377,17 @@ uint32_t ListEntitiesClimateResponse::calculate_size() const {
   size += ProtoSize::calc_bool(1, this->supports_current_temperature);
   size += ProtoSize::calc_bool(1, this->supports_two_point_target_temperature);
   if (!this->supported_modes->empty()) {
-    for (const auto &it : *this->supported_modes) {
-      size += 2;
-    }
+    size += this->supported_modes->size() * 2;
   }
   size += ProtoSize::calc_float(1, this->visual_min_temperature);
   size += ProtoSize::calc_float(1, this->visual_max_temperature);
   size += ProtoSize::calc_float(1, this->visual_target_temperature_step);
   size += ProtoSize::calc_bool(1, this->supports_action);
   if (!this->supported_fan_modes->empty()) {
-    for (const auto &it : *this->supported_fan_modes) {
-      size += 2;
-    }
+    size += this->supported_fan_modes->size() * 2;
   }
   if (!this->supported_swing_modes->empty()) {
-    for (const auto &it : *this->supported_swing_modes) {
-      size += 2;
-    }
+    size += this->supported_swing_modes->size() * 2;
   }
   if (!this->supported_custom_fan_modes->empty()) {
     for (const char *it : *this->supported_custom_fan_modes) {
@@ -1403,9 +1395,7 @@ uint32_t ListEntitiesClimateResponse::calculate_size() const {
     }
   }
   if (!this->supported_presets->empty()) {
-    for (const auto &it : *this->supported_presets) {
-      size += 3;
-    }
+    size += this->supported_presets->size() * 3;
   }
   if (!this->supported_custom_presets->empty()) {
     for (const char *it : *this->supported_custom_presets) {
@@ -1598,9 +1588,7 @@ uint32_t ListEntitiesWaterHeaterResponse::calculate_size() const {
   size += ProtoSize::calc_float(1, this->max_temperature);
   size += ProtoSize::calc_float(1, this->target_temperature_step);
   if (!this->supported_modes->empty()) {
-    for (const auto &it : *this->supported_modes) {
-      size += 2;
-    }
+    size += this->supported_modes->size() * 2;
   }
   size += ProtoSize::calc_uint32(1, this->supported_features);
   return size;
diff --git a/script/api_protobuf/api_protobuf.py b/script/api_protobuf/api_protobuf.py
index 2f2b5f4baa..ac8845ae5f 100755
--- a/script/api_protobuf/api_protobuf.py
+++ b/script/api_protobuf/api_protobuf.py
@@ -1907,17 +1907,27 @@ class RepeatedTypeInfo(TypeInfo):
             size_expr = f"{name}->size()" if self._use_pointer else f"{name}.size()"
             o += f"  size += {size_expr} * {bytes_per_element};\n"
         else:
-            # Other types need the actual value
+            # Check if inner type produces a constant size (doesn't depend on value)
+            inner_size = self._ti.get_size_calculation("it", True)
+            if "it" not in inner_size:
+                # Constant size per element — use multiply instead of loop
+                # Extract the constant from "size += N;"
+                const_val = (
+                    inner_size.strip().removeprefix("size += ").removesuffix(";")
+                )
+                size_expr = f"{name}->size()" if self._use_pointer else f"{name}.size()"
+                o += f"  size += {size_expr} * {const_val};\n"
             # Special handling for const char* elements
-            if self._use_pointer and "const char" in self._container_no_template:
+            elif self._use_pointer and "const char" in self._container_no_template:
                 field_id_size = self.calculate_field_id_size()
                 o += f"  for (const char *it : {container_ref}) {{\n"
                 o += f"    size += ProtoSize::calc_length_force({field_id_size}, strlen(it));\n"
+                o += "  }\n"
             else:
                 auto_ref = "" if self._ti_is_bool else "&"
                 o += f"  for (const auto {auto_ref}it : {container_ref}) {{\n"
-                o += f"    {self._ti.get_size_calculation('it', True)}\n"
-            o += "  }\n"
+                o += f"    {inner_size}\n"
+                o += "  }\n"
 
         o += "}"
         return o