diff --git a/esphome/components/json/json_util.cpp b/esphome/components/json/json_util.cpp
index 9a159fb28a..cb5dfe6e2d 100644
--- a/esphome/components/json/json_util.cpp
+++ b/esphome/components/json/json_util.cpp
@@ -70,7 +70,7 @@ SerializationBuffer<> JsonBuilder::serialize() {
   // directly in the caller's stack frame, eliminating the move constructor call entirely.
   //
   // WITHOUT NRVO: Each return would trigger SerializationBuffer's move constructor, which
-  // must memcpy up to 768 bytes of stack buffer content. This happens on EVERY JSON
+  // must memcpy up to 512 bytes of stack buffer content. This happens on EVERY JSON
   // serialization (sensor updates, web server responses, MQTT publishes, etc.).
   //
   // WITH NRVO: Zero memcpy, zero move constructor overhead. The buffer lives directly
@@ -89,7 +89,7 @@ SerializationBuffer<> JsonBuilder::serialize() {
   //     Should show only destructor, NOT move constructor
   //
   // Why we avoid measureJson(): It instantiates DummyWriter templates adding ~1KB flash.
-  // Instead, try stack buffer first. 768 bytes covers 99.9% of JSON payloads (sensors ~200B,
+  // Instead, try stack buffer first. 512 bytes covers 99.9% of JSON payloads (sensors ~200B,
   // lights ~170B, climate ~700B). Only entities with 40+ options exceed this.
   //
   // ===========================================================================================
diff --git a/esphome/components/json/json_util.h b/esphome/components/json/json_util.h
index 95a9d25194..3ea551bc8e 100644
--- a/esphome/components/json/json_util.h
+++ b/esphome/components/json/json_util.h
@@ -17,9 +17,9 @@ namespace esphome {
 namespace json {
 
 /// Buffer for JSON serialization that uses stack allocation for small payloads.
-/// Template parameter STACK_SIZE specifies the stack buffer size (default 768 bytes).
+/// Template parameter STACK_SIZE specifies the stack buffer size (default 512 bytes).
 /// Supports move semantics for efficient return-by-value.
-template<size_t STACK_SIZE = 768> class SerializationBuffer {
+template<size_t STACK_SIZE = 512> class SerializationBuffer {
  public:
   static constexpr size_t BUFFER_SIZE = STACK_SIZE;  ///< Stack buffer size for this instantiation
 
@@ -175,7 +175,7 @@ class JsonBuilder {
   }
 
   /// Serialize the JSON document to a SerializationBuffer (stack-first allocation)
-  /// Uses 768-byte stack buffer by default, falls back to heap for larger JSON
+  /// Uses 512-byte stack buffer by default, falls back to heap for larger JSON
   SerializationBuffer<> serialize();
 
  private: