diff --git a/esphome/components/web_server_base/__init__.py b/esphome/components/web_server_base/__init__.py
index 4cf76eba0e..d5d75b395d 100644
--- a/esphome/components/web_server_base/__init__.py
+++ b/esphome/components/web_server_base/__init__.py
@@ -34,6 +34,8 @@ async def to_code(config):
     cg.add(cg.RawExpression(f"{web_server_base_ns}::global_web_server_base = {var}"))
 
     if CORE.is_esp32:
+        # Count for StaticVector in web_server_idf - matches headers added in init()
+        cg.add_define("WEB_SERVER_DEFAULT_HEADERS_COUNT", 1)
         return
 
     if CORE.using_arduino:
diff --git a/esphome/components/web_server_base/web_server_base.h b/esphome/components/web_server_base/web_server_base.h
index 7e95e00f29..0c25467f1b 100644
--- a/esphome/components/web_server_base/web_server_base.h
+++ b/esphome/components/web_server_base/web_server_base.h
@@ -100,6 +100,8 @@ class WebServerBase : public Component {
     }
     this->server_ = std::make_unique<AsyncWebServer>(this->port_);
     // All content is controlled and created by user - so allowing all origins is fine here.
+    // NOTE: Currently 1 header. If more are added, update in __init__.py:
+    //   cg.add_define("WEB_SERVER_DEFAULT_HEADERS_COUNT", 1)
     DefaultHeaders::Instance().addHeader(ESPHOME_F("Access-Control-Allow-Origin"), ESPHOME_F("*"));
     this->server_->begin();
 
diff --git a/esphome/components/web_server_idf/web_server_idf.h b/esphome/components/web_server_idf/web_server_idf.h
index bce2467ade..8c37690c1c 100644
--- a/esphome/components/web_server_idf/web_server_idf.h
+++ b/esphome/components/web_server_idf/web_server_idf.h
@@ -2,6 +2,7 @@
 #ifdef USE_ESP32
 
 #include "esphome/core/defines.h"
+#include "esphome/core/helpers.h"
 #include <esp_http_server.h>
 
 #include <atomic>
@@ -345,7 +346,8 @@ class DefaultHeaders {
   static DefaultHeaders &Instance();
 
  protected:
-  std::vector<HttpHeader> headers_;
+  // Stack-allocated, no reallocation machinery. Count defined in web_server_base where headers are added.
+  StaticVector<HttpHeader, WEB_SERVER_DEFAULT_HEADERS_COUNT> headers_;
 };
 
 }  // namespace web_server_idf
diff --git a/esphome/core/defines.h b/esphome/core/defines.h
index ae94f6ef5f..adb2921b68 100644
--- a/esphome/core/defines.h
+++ b/esphome/core/defines.h
@@ -213,6 +213,7 @@
 #define USE_WEBSERVER_PORT 80  // NOLINT
 #define USE_WEBSERVER_GZIP
 #define USE_WEBSERVER_SORTING
+#define WEB_SERVER_DEFAULT_HEADERS_COUNT 1
 #define USE_CAPTIVE_PORTAL_GZIP
 #define USE_WIFI_11KV_SUPPORT
 #define USE_WIFI_FAST_CONNECT