diff --git a/esphome/espidf/size_summary.py b/esphome/espidf/size_summary.py
index 06e0ecba5c..79f8d48848 100644
--- a/esphome/espidf/size_summary.py
+++ b/esphome/espidf/size_summary.py
@@ -10,10 +10,12 @@ byte-identical to PlatformIO's output:
 
 The format matches ``script/ci_memory_impact_extract.py`` so CI memory
 analysis works unchanged on native ESP-IDF builds. RAM usage comes from
-the DRAM (or unified DIRAM) region of the linker map; Flash used is the
-size of the app ``.bin`` on disk, which includes esptool's 16-byte
-image padding and appended SHA-256, so it reads slightly above the
-map-derived ``Total image size`` line and moves in 16-byte steps.
+the DRAM (or unified DIRAM) region of the linker map. Flash used is the
+json2 ``total_size`` field when present (esp-idf-size >= 2.1, the exact
+map-derived figure matching the ``Total image size`` line); older 1.x
+json2 lacks it, and the fallback is the size of the app ``.bin`` on
+disk, which includes esptool's 16-byte image padding and appended
+SHA-256 so it reads slightly high and moves in 16-byte steps.
 Flash total is taken from
 ``partitions.csv`` using PlatformIO's rule (first app partition whose
 subtype is ``factory`` or ``ota_0``; see
@@ -101,8 +103,13 @@ def print_summary(size_json: Path, partitions_csv: Path, firmware_bin: Path) ->
     if ram_total and ram_used is not None:
         print_size_line("RAM", ram_used, ram_total)
 
+    # esp-idf-size >= 2.1 (IDF >= 6.0) reports the exact map-derived image
+    # size in json2; older 1.x omits it, so fall back to the padded on-disk
+    # .bin size.
+    flash_used = data.get("total_size")
     try:
-        flash_used = firmware_bin.stat().st_size
+        if flash_used is None:
+            flash_used = firmware_bin.stat().st_size
         app_size = _find_app_partition_size(partitions_csv)
     except (OSError, ValueError) as e:
         _LOGGER.debug("Skipping Flash summary: %s", e)
diff --git a/tests/unit_tests/test_size_summary.py b/tests/unit_tests/test_size_summary.py
index ff5c7b95c1..0eb876da99 100644
--- a/tests/unit_tests/test_size_summary.py
+++ b/tests/unit_tests/test_size_summary.py
@@ -28,9 +28,11 @@ def _write_partitions(tmp_path: Path) -> Path:
 
 
 def _esp32_size_data() -> dict:
-    """Synthetic json2 esp_idf_size.json for the original ESP32 (split IRAM/DRAM)."""
+    """Synthetic json2 for the original ESP32 (split IRAM/DRAM), in the
+    esp-idf-size >= 2.1 shape that carries ``total_size``."""
     return {
         "version": "1.1",
+        "total_size": 827455,
         "layout": [
             {
                 "name": "DRAM",
@@ -57,7 +59,8 @@ def _esp32_size_data() -> dict:
 
 
 def _s3_size_data() -> dict:
-    """Synthetic json2 esp_idf_size.json for ESP32-S3 (unified DIRAM)."""
+    """Synthetic json2 for ESP32-S3 (unified DIRAM), in the esp-idf-size 1.x
+    shape without ``total_size``."""
     return {
         "version": "1.1",
         "layout": [
@@ -146,27 +149,40 @@ def test_print_summary_handles_no_layout(
     assert capsys.readouterr().out == ""
 
 
-def test_print_summary_flash_line(
+def test_print_summary_flash_line_prefers_total_size(
     tmp_path: Path, capsys: pytest.CaptureFixture[str]
 ) -> None:
-    """A partition table with an app row yields the Flash line in the exact
-    padded shape script/ci_memory_impact_extract.py greps."""
+    """With ``total_size`` in the json, the exact figure wins over the padded
+    bin size, in the exact shape script/ci_memory_impact_extract.py greps."""
     size_json = _write_size_json(tmp_path, _esp32_size_data())
     partitions = _write_partitions(tmp_path)
     firmware_bin = tmp_path / "firmware.bin"
-    firmware_bin.write_bytes(b"\x00" * 827455)
+    firmware_bin.write_bytes(b"\x00" * 999999)
     print_summary(size_json, partitions, firmware_bin)
     out = capsys.readouterr().out
     assert "Flash: " in out
     assert "(used 827455 bytes from 1835008 bytes)" in out
 
 
+def test_print_summary_flash_line_falls_back_to_bin_size(
+    tmp_path: Path, capsys: pytest.CaptureFixture[str]
+) -> None:
+    """A 1.x json without ``total_size`` uses the on-disk bin size."""
+    size_json = _write_size_json(tmp_path, _s3_size_data())
+    partitions = _write_partitions(tmp_path)
+    firmware_bin = tmp_path / "firmware.bin"
+    firmware_bin.write_bytes(b"\x00" * 724224)
+    print_summary(size_json, partitions, firmware_bin)
+    out = capsys.readouterr().out
+    assert "(used 724224 bytes from 1835008 bytes)" in out
+
+
 @pytest.mark.parametrize("missing", ["bin", "partitions"])
 def test_print_summary_skips_flash_on_missing_input(
     missing: str, tmp_path: Path, capsys: pytest.CaptureFixture[str]
 ) -> None:
     """A missing firmware bin or partitions.csv skips the Flash line, not the RAM line."""
-    size_json = _write_size_json(tmp_path, _esp32_size_data())
+    size_json = _write_size_json(tmp_path, _s3_size_data())
     firmware_bin = tmp_path / "firmware.bin"
     if missing == "bin":
         _write_partitions(tmp_path)