diff --git a/firmware/fs/README.md b/firmware/fs/README.md
new file mode 100644
index 0000000..49f3b66
--- /dev/null
+++ b/firmware/fs/README.md
@@ -0,0 +1,86 @@
+# FS Tooling
+
+This directory contains the tooling to build and flash the external LittleFS image used by the firmware.
+
+## Python Version
+
+Use Python 3.11.
+
+The filesystem/audio build tool is currently tested with Python 3.11.
+Python 3.13 is not supported at the moment, especially on Windows, because some dependencies in the TTS toolchain may fall back to source builds and fail to install.
+
+In particular, the dependency chain around `kokoro`, `spacy`, `thinc`, and `blis` may fail to install on Windows when no compatible wheels are available.
+
+## Install Dependencies
+
+`ffmpeg` is required in addition to the Python packages.
+
+```sh
+python3.11 -m venv venv
+. venv/bin/activate
+pip install -r requirements.txt
+```
+
+On Windows:
+
+```bat
+py -3.11 -m venv venv
+venv\Scripts\activate
+pip install -r requirements.txt
+```
+
+## Build LittleFS Image
+
+```sh
+./venv/bin/python build_lfs_audio.py
+```
+
+Example with imported WAV files and a custom system prompt YAML:
+
+```sh
+./venv/bin/python build_lfs_audio.py \
+	--wav-dir ./my_wavs \
+	--sys-yaml ./sys_prompts.yaml
+```
+
+Notes:
+
+- `--wav-dir` imports all `.wav` files from the given directory into `/lfs/a`
+- `--sys-yaml` overrides the default TTS prompt list for `/lfs/sys`
+- generated audio is converted to mono 16 kHz PCM before it is written into the LittleFS image
+
+This generates:
+
+- `lfs_external_flash.hex`
+
+The default image layout is aligned to a 4 KiB flash page layout.
+
+After the build, the script also prints a usage summary for `/lfs/sys`, `/lfs/a`, and the combined image.
+
+Example:
+
+```text
+Usage summary:
+	sys: files=4, raw=48.0 KiB, fs=56.0 KiB (14 blocks, standalone estimate)
+	audio: files=12, raw=224.0 KiB, fs=264.0 KiB (66 blocks, standalone estimate)
+	total: raw=272.0 KiB, fs=300.0 KiB (75 blocks in combined image)
+```
+
+`raw` is the sum of file sizes in the staging tree.
+`fs` is the estimated or measured LittleFS space usage with the configured block size.
+
+## Flash Image
+
+On macOS/Linux:
+
+```sh
+./program.sh
+```
+
+On Windows:
+
+```bat
+program.bat
+```
+
+Both scripts use paths relative to their own location, so they can be started from any working directory.
\ No newline at end of file
diff --git a/firmware/fs/build_lfs_audio.py b/firmware/fs/build_lfs_audio.py
index e2d55a5..4bd5f5c 100644
--- a/firmware/fs/build_lfs_audio.py
+++ b/firmware/fs/build_lfs_audio.py
@@ -15,6 +15,8 @@ DEFAULT_SAMPLE_RATE = 16000
 DEFAULT_VOICE = "af_bella"
 DEFAULT_BLOCK_SIZE = 4096
 DEFAULT_BLOCK_COUNT = 2048
+DEFAULT_READ_SIZE = 512
+DEFAULT_LOOKAHEAD_SIZE = 256
 DEFAULT_FILTERS = [
     "highpass=f=120",
     "lowpass=f=6000",
@@ -26,6 +28,7 @@ DEFAULT_SYS_PROMPTS = [
     {"id": "404", "text": "No sound sample was found on the device."},
     {"id": "update", "text": "Firmware updated. Awaiting confirmation."},
     {"id": "confirm", "text": "State confirmed."},
+    {"id": "voltest", "text": "Volume test. This is a sample of the current volume level."},
 ]
 
 
@@ -129,18 +132,32 @@ def add_files_recursive(fs: LittleFS, local_path: Path, lfs_path: str = "/") ->
             add_files_recursive(fs, item, target_path)
 
 
-def build_littlefs_hex(source_folder: Path, output_hex: Path, block_size: int, block_count: int, start_addr: int) -> None:
+def build_littlefs_image(source_folder: Path, block_size: int, block_count: int) -> tuple[LittleFS, int]:
     fs = LittleFS(
         block_size=block_size,
         block_count=block_count,
-        read_size=256,
+        read_size=DEFAULT_READ_SIZE,
         prog_size=256,
-        lookahead_size=512,
+        lookahead_size=DEFAULT_LOOKAHEAD_SIZE,
         cache_size=4096,
     )
 
     add_files_recursive(fs, source_folder)
 
+    used_blocks = 0
+    lfs_buffer = fs.context.buffer
+    for idx in range(block_count):
+        offset = idx * block_size
+        block_data = lfs_buffer[offset : offset + block_size]
+        if any(byte != 0xFF for byte in block_data):
+            used_blocks += 1
+
+    return fs, used_blocks
+
+
+def build_littlefs_hex(source_folder: Path, output_hex: Path, block_size: int, block_count: int, start_addr: int) -> int:
+    fs, used_blocks = build_littlefs_image(source_folder, block_size, block_count)
+
     ih = IntelHex()
     lfs_buffer = fs.context.buffer
 
@@ -151,6 +168,42 @@ def build_littlefs_hex(source_folder: Path, output_hex: Path, block_size: int, b
             ih.frombytes(block_data, offset=start_addr + offset)
 
     ih.tofile(str(output_hex), format="hex")
+    return used_blocks
+
+
+def summarize_directory(directory: Path) -> tuple[int, int]:
+    if not directory.exists():
+        return 0, 0
+
+    file_count = 0
+    raw_bytes = 0
+    for file_path in directory.rglob("*"):
+        if file_path.is_file():
+            file_count += 1
+            raw_bytes += file_path.stat().st_size
+
+    return file_count, raw_bytes
+
+
+def format_bytes(size: int) -> str:
+    units = ["B", "KiB", "MiB", "GiB"]
+    value = float(size)
+    for unit in units:
+        if value < 1024.0 or unit == units[-1]:
+            if unit == "B":
+                return f"{int(value)} {unit}"
+            return f"{value:.1f} {unit}"
+        value /= 1024.0
+
+
+def report_directory_usage(label: str, directory: Path, block_size: int, block_count: int) -> None:
+    file_count, raw_bytes = summarize_directory(directory)
+    _, used_blocks = build_littlefs_image(directory, block_size, block_count)
+    fs_bytes = used_blocks * block_size
+    print(
+        f"  {label}: files={file_count}, raw={format_bytes(raw_bytes)}, "
+        f"fs={format_bytes(fs_bytes)} ({used_blocks} blocks, standalone estimate)"
+    )
 
 
 def parse_args() -> argparse.Namespace:
@@ -203,7 +256,7 @@ def main() -> None:
     tts_count = build_sys_tts(prompts, out_sys, args.sample_rate)
     wav_count = import_wavs_to_a(wav_dir, out_a, args.sample_rate)
 
-    build_littlefs_hex(
+    total_used_blocks = build_littlefs_hex(
         source_folder=staging_root,
         output_hex=output_hex,
         block_size=args.block_size,
@@ -212,6 +265,14 @@ def main() -> None:
     )
 
     print(f"Done. TTS assets: {tts_count}, WAV imports: {wav_count}, HEX: {output_hex}")
+    print("Usage summary:")
+    report_directory_usage("sys", out_sys, args.block_size, args.block_count)
+    report_directory_usage("audio", out_a, args.block_size, args.block_count)
+    print(
+        f"  total: raw={format_bytes(summarize_directory(staging_root)[1])}, "
+        f"fs={format_bytes(total_used_blocks * args.block_size)} "
+        f"({total_used_blocks} blocks in combined image)"
+    )
 
     if not args.keep_staging and staging_root.exists():
         shutil.rmtree(staging_root)
diff --git a/firmware/libs/fs_mgmt/Kconfig b/firmware/libs/fs_mgmt/Kconfig
index cbe2f8a..56d0dd2 100644
--- a/firmware/libs/fs_mgmt/Kconfig
+++ b/firmware/libs/fs_mgmt/Kconfig
@@ -58,13 +58,13 @@ if FS_MGMT
     endif # SOC_SERIES_NRF52X
 
     config FS_LITTLEFS_READ_SIZE
-        default 256
+        default 512
     config FS_LITTLEFS_PROG_SIZE
         default 256
     config FS_LITTLEFS_CACHE_SIZE
         default 4096
     config FS_LITTLEFS_LOOKAHEAD_SIZE
-        default 512
+        default 256
 
     module = FS_MGMT
     module-str = fs_mgmt