diff --git a/esphome/components/api/api_pb2.cpp b/esphome/components/api/api_pb2.cpp
index 6ef7ca4d3f..9ba24449d7 100644
--- a/esphome/components/api/api_pb2.cpp
+++ b/esphome/components/api/api_pb2.cpp
@@ -234,7 +234,7 @@ uint32_t ListEntitiesBinarySensorResponse::calculate_size() const {
   size += ProtoSize::calc_bool(1, this->is_status_binary_sensor);
   size += ProtoSize::calc_bool(1, this->disabled_by_default);
 #ifdef USE_ENTITY_ICON
-  size += this->icon.size() ? 2 + this->icon.size() : 0;
+  size += !this->icon.empty() ? 2 + this->icon.size() : 0;
 #endif
   size += ProtoSize::calc_uint32(1, static_cast<uint32_t>(this->entity_category));
 #ifdef USE_DEVICES
@@ -295,7 +295,7 @@ uint32_t ListEntitiesCoverResponse::calculate_size() const {
   size += ProtoSize::calc_length(1, this->device_class.size());
   size += ProtoSize::calc_bool(1, this->disabled_by_default);
 #ifdef USE_ENTITY_ICON
-  size += this->icon.size() ? 2 + this->icon.size() : 0;
+  size += !this->icon.empty() ? 2 + this->icon.size() : 0;
 #endif
   size += ProtoSize::calc_uint32(1, static_cast<uint32_t>(this->entity_category));
   size += ProtoSize::calc_bool(1, this->supports_stop);
@@ -398,7 +398,7 @@ uint32_t ListEntitiesFanResponse::calculate_size() const {
   size += ProtoSize::calc_int32(1, this->supported_speed_count);
   size += ProtoSize::calc_bool(1, this->disabled_by_default);
 #ifdef USE_ENTITY_ICON
-  size += this->icon.size() ? 2 + this->icon.size() : 0;
+  size += !this->icon.empty() ? 2 + this->icon.size() : 0;
 #endif
   size += ProtoSize::calc_uint32(1, static_cast<uint32_t>(this->entity_category));
   if (!this->supported_preset_modes->empty()) {
@@ -541,7 +541,7 @@ uint32_t ListEntitiesLightResponse::calculate_size() const {
   }
   size += ProtoSize::calc_bool(1, this->disabled_by_default);
 #ifdef USE_ENTITY_ICON
-  size += this->icon.size() ? 2 + this->icon.size() : 0;
+  size += !this->icon.empty() ? 2 + this->icon.size() : 0;
 #endif
   size += ProtoSize::calc_uint32(1, static_cast<uint32_t>(this->entity_category));
 #ifdef USE_DEVICES
@@ -725,7 +725,7 @@ uint32_t ListEntitiesSensorResponse::calculate_size() const {
   size += 5;
   size += 2 + this->name.size();
 #ifdef USE_ENTITY_ICON
-  size += this->icon.size() ? 2 + this->icon.size() : 0;
+  size += !this->icon.empty() ? 2 + this->icon.size() : 0;
 #endif
   size += ProtoSize::calc_length(1, this->unit_of_measurement.size());
   size += ProtoSize::calc_int32(1, this->accuracy_decimals);
@@ -784,7 +784,7 @@ uint32_t ListEntitiesSwitchResponse::calculate_size() const {
   size += 5;
   size += 2 + this->name.size();
 #ifdef USE_ENTITY_ICON
-  size += this->icon.size() ? 2 + this->icon.size() : 0;
+  size += !this->icon.empty() ? 2 + this->icon.size() : 0;
 #endif
   size += ProtoSize::calc_bool(1, this->assumed_state);
   size += ProtoSize::calc_bool(1, this->disabled_by_default);
@@ -862,7 +862,7 @@ uint32_t ListEntitiesTextSensorResponse::calculate_size() const {
   size += 5;
   size += 2 + this->name.size();
 #ifdef USE_ENTITY_ICON
-  size += this->icon.size() ? 2 + this->icon.size() : 0;
+  size += !this->icon.empty() ? 2 + this->icon.size() : 0;
 #endif
   size += ProtoSize::calc_bool(1, this->disabled_by_default);
   size += ProtoSize::calc_uint32(1, static_cast<uint32_t>(this->entity_category));
@@ -1319,7 +1319,7 @@ uint32_t ListEntitiesCameraResponse::calculate_size() const {
   size += 2 + this->name.size();
   size += ProtoSize::calc_bool(1, this->disabled_by_default);
 #ifdef USE_ENTITY_ICON
-  size += this->icon.size() ? 2 + this->icon.size() : 0;
+  size += !this->icon.empty() ? 2 + this->icon.size() : 0;
 #endif
   size += ProtoSize::calc_uint32(1, static_cast<uint32_t>(this->entity_category));
 #ifdef USE_DEVICES
@@ -1450,7 +1450,7 @@ uint32_t ListEntitiesClimateResponse::calculate_size() const {
   }
   size += ProtoSize::calc_bool(2, this->disabled_by_default);
 #ifdef USE_ENTITY_ICON
-  size += this->icon.size() ? 3 + this->icon.size() : 0;
+  size += !this->icon.empty() ? 3 + this->icon.size() : 0;
 #endif
   size += ProtoSize::calc_uint32(2, static_cast<uint32_t>(this->entity_category));
   size += ProtoSize::calc_float(2, this->visual_current_temperature_step);
@@ -1627,7 +1627,7 @@ uint32_t ListEntitiesWaterHeaterResponse::calculate_size() const {
   size += 5;
   size += 2 + this->name.size();
 #ifdef USE_ENTITY_ICON
-  size += this->icon.size() ? 2 + this->icon.size() : 0;
+  size += !this->icon.empty() ? 2 + this->icon.size() : 0;
 #endif
   size += ProtoSize::calc_bool(1, this->disabled_by_default);
   size += ProtoSize::calc_uint32(1, static_cast<uint32_t>(this->entity_category));
@@ -1742,7 +1742,7 @@ uint32_t ListEntitiesNumberResponse::calculate_size() const {
   size += 5;
   size += 2 + this->name.size();
 #ifdef USE_ENTITY_ICON
-  size += this->icon.size() ? 2 + this->icon.size() : 0;
+  size += !this->icon.empty() ? 2 + this->icon.size() : 0;
 #endif
   size += ProtoSize::calc_float(1, this->min_value);
   size += ProtoSize::calc_float(1, this->max_value);
@@ -1828,7 +1828,7 @@ uint32_t ListEntitiesSelectResponse::calculate_size() const {
   size += 5;
   size += 2 + this->name.size();
 #ifdef USE_ENTITY_ICON
-  size += this->icon.size() ? 2 + this->icon.size() : 0;
+  size += !this->icon.empty() ? 2 + this->icon.size() : 0;
 #endif
   if (!this->options->empty()) {
     for (const char *it : *this->options) {
@@ -1923,7 +1923,7 @@ uint32_t ListEntitiesSirenResponse::calculate_size() const {
   size += 5;
   size += 2 + this->name.size();
 #ifdef USE_ENTITY_ICON
-  size += this->icon.size() ? 2 + this->icon.size() : 0;
+  size += !this->icon.empty() ? 2 + this->icon.size() : 0;
 #endif
   size += ProtoSize::calc_bool(1, this->disabled_by_default);
   if (!this->tones->empty()) {
@@ -2038,7 +2038,7 @@ uint32_t ListEntitiesLockResponse::calculate_size() const {
   size += 5;
   size += 2 + this->name.size();
 #ifdef USE_ENTITY_ICON
-  size += this->icon.size() ? 2 + this->icon.size() : 0;
+  size += !this->icon.empty() ? 2 + this->icon.size() : 0;
 #endif
   size += ProtoSize::calc_bool(1, this->disabled_by_default);
   size += ProtoSize::calc_uint32(1, static_cast<uint32_t>(this->entity_category));
@@ -2132,7 +2132,7 @@ uint32_t ListEntitiesButtonResponse::calculate_size() const {
   size += 5;
   size += 2 + this->name.size();
 #ifdef USE_ENTITY_ICON
-  size += this->icon.size() ? 2 + this->icon.size() : 0;
+  size += !this->icon.empty() ? 2 + this->icon.size() : 0;
 #endif
   size += ProtoSize::calc_bool(1, this->disabled_by_default);
   size += ProtoSize::calc_uint32(1, static_cast<uint32_t>(this->entity_category));
@@ -2210,7 +2210,7 @@ uint32_t ListEntitiesMediaPlayerResponse::calculate_size() const {
   size += 5;
   size += 2 + this->name.size();
 #ifdef USE_ENTITY_ICON
-  size += this->icon.size() ? 2 + this->icon.size() : 0;
+  size += !this->icon.empty() ? 2 + this->icon.size() : 0;
 #endif
   size += ProtoSize::calc_bool(1, this->disabled_by_default);
   size += ProtoSize::calc_uint32(1, static_cast<uint32_t>(this->entity_category));
@@ -3034,7 +3034,7 @@ uint32_t ListEntitiesAlarmControlPanelResponse::calculate_size() const {
   size += 5;
   size += 2 + this->name.size();
 #ifdef USE_ENTITY_ICON
-  size += this->icon.size() ? 2 + this->icon.size() : 0;
+  size += !this->icon.empty() ? 2 + this->icon.size() : 0;
 #endif
   size += ProtoSize::calc_bool(1, this->disabled_by_default);
   size += ProtoSize::calc_uint32(1, static_cast<uint32_t>(this->entity_category));
@@ -3127,7 +3127,7 @@ uint32_t ListEntitiesTextResponse::calculate_size() const {
   size += 5;
   size += 2 + this->name.size();
 #ifdef USE_ENTITY_ICON
-  size += this->icon.size() ? 2 + this->icon.size() : 0;
+  size += !this->icon.empty() ? 2 + this->icon.size() : 0;
 #endif
   size += ProtoSize::calc_bool(1, this->disabled_by_default);
   size += ProtoSize::calc_uint32(1, static_cast<uint32_t>(this->entity_category));
@@ -3216,7 +3216,7 @@ uint32_t ListEntitiesDateResponse::calculate_size() const {
   size += 5;
   size += 2 + this->name.size();
 #ifdef USE_ENTITY_ICON
-  size += this->icon.size() ? 2 + this->icon.size() : 0;
+  size += !this->icon.empty() ? 2 + this->icon.size() : 0;
 #endif
   size += ProtoSize::calc_bool(1, this->disabled_by_default);
   size += ProtoSize::calc_uint32(1, static_cast<uint32_t>(this->entity_category));
@@ -3303,7 +3303,7 @@ uint32_t ListEntitiesTimeResponse::calculate_size() const {
   size += 5;
   size += 2 + this->name.size();
 #ifdef USE_ENTITY_ICON
-  size += this->icon.size() ? 2 + this->icon.size() : 0;
+  size += !this->icon.empty() ? 2 + this->icon.size() : 0;
 #endif
   size += ProtoSize::calc_bool(1, this->disabled_by_default);
   size += ProtoSize::calc_uint32(1, static_cast<uint32_t>(this->entity_category));
@@ -3394,7 +3394,7 @@ uint32_t ListEntitiesEventResponse::calculate_size() const {
   size += 5;
   size += 2 + this->name.size();
 #ifdef USE_ENTITY_ICON
-  size += this->icon.size() ? 2 + this->icon.size() : 0;
+  size += !this->icon.empty() ? 2 + this->icon.size() : 0;
 #endif
   size += ProtoSize::calc_bool(1, this->disabled_by_default);
   size += ProtoSize::calc_uint32(1, static_cast<uint32_t>(this->entity_category));
@@ -3454,7 +3454,7 @@ uint32_t ListEntitiesValveResponse::calculate_size() const {
   size += 5;
   size += 2 + this->name.size();
 #ifdef USE_ENTITY_ICON
-  size += this->icon.size() ? 2 + this->icon.size() : 0;
+  size += !this->icon.empty() ? 2 + this->icon.size() : 0;
 #endif
   size += ProtoSize::calc_bool(1, this->disabled_by_default);
   size += ProtoSize::calc_uint32(1, static_cast<uint32_t>(this->entity_category));
@@ -3541,7 +3541,7 @@ uint32_t ListEntitiesDateTimeResponse::calculate_size() const {
   size += 5;
   size += 2 + this->name.size();
 #ifdef USE_ENTITY_ICON
-  size += this->icon.size() ? 2 + this->icon.size() : 0;
+  size += !this->icon.empty() ? 2 + this->icon.size() : 0;
 #endif
   size += ProtoSize::calc_bool(1, this->disabled_by_default);
   size += ProtoSize::calc_uint32(1, static_cast<uint32_t>(this->entity_category));
@@ -3619,7 +3619,7 @@ uint32_t ListEntitiesUpdateResponse::calculate_size() const {
   size += 5;
   size += 2 + this->name.size();
 #ifdef USE_ENTITY_ICON
-  size += this->icon.size() ? 2 + this->icon.size() : 0;
+  size += !this->icon.empty() ? 2 + this->icon.size() : 0;
 #endif
   size += ProtoSize::calc_bool(1, this->disabled_by_default);
   size += ProtoSize::calc_uint32(1, static_cast<uint32_t>(this->entity_category));
@@ -3765,7 +3765,7 @@ uint32_t ListEntitiesInfraredResponse::calculate_size() const {
   size += 5;
   size += 2 + this->name.size();
 #ifdef USE_ENTITY_ICON
-  size += this->icon.size() ? 2 + this->icon.size() : 0;
+  size += !this->icon.empty() ? 2 + this->icon.size() : 0;
 #endif
   size += ProtoSize::calc_bool(1, this->disabled_by_default);
   size += ProtoSize::calc_uint32(1, static_cast<uint32_t>(this->entity_category));
diff --git a/script/api_protobuf/api_protobuf.py b/script/api_protobuf/api_protobuf.py
index a0335ff404..208412b62b 100755
--- a/script/api_protobuf/api_protobuf.py
+++ b/script/api_protobuf/api_protobuf.py
@@ -376,7 +376,11 @@ class TypeInfo(ABC):
         return f"size += ProtoSize::{method}({field_id_size}, {value});"
 
     def _get_single_byte_varint_size(
-        self, name: str, force: bool, extra_expr: str | None = None
+        self,
+        name: str,
+        force: bool,
+        extra_expr: str | None = None,
+        zero_check: str | None = None,
     ) -> str:
         """Size calculation when the varint is guaranteed to be 1 byte.
 
@@ -387,12 +391,14 @@ class TypeInfo(ABC):
             name: Expression to check for zero (non-force only)
             force: Whether to skip the zero check
             extra_expr: Additional variable expression to add (e.g., data length)
+            zero_check: Override expression for the zero check (e.g., "!x.empty()")
         """
         fixed = self.calculate_field_id_size() + 1
         size_expr = f"{fixed} + {extra_expr}" if extra_expr else str(fixed)
         if force:
             return f"size += {size_expr};"
-        return f"size += {name} ? {size_expr} : 0;"
+        check = zero_check or name
+        return f"size += {check} ? {size_expr} : 0;"
 
     @abstractmethod
     def get_size_calculation(self, name: str, force: bool = False) -> str:
@@ -1100,7 +1106,10 @@ class PointerToStringBufferType(PointerToBufferTypeBase):
         max_len = self.max_data_length
         if max_len is not None and max_len < 128:
             return self._get_single_byte_varint_size(
-                size_field, force, extra_expr=size_field
+                size_field,
+                force,
+                extra_expr=size_field,
+                zero_check=f"!this->{self.field_name}.empty()",
             )
         return self._get_simple_size_calculation(size_field, force, "length")