diff --git a/README.md b/README.md
index 4957eec3..e7f95632 100644
--- a/README.md
+++ b/README.md
@@ -165,6 +165,26 @@ If seconds are too large, set `minimum_unit` to milliseconds or microseconds:
 '976.6K'
 ```
 
+The same formatter is available from the command line:
+
+```console
+$ humanize naturalsize 8589934592
+8.6 GB
+$ python -m humanize naturalsize --binary 8589934592
+8.0 GiB
+$ humanize naturalsize --gnu --format "%.2f" 8589934592
+8.00G
+```
+
+When the value is omitted, the command reads one byte count per line from standard
+input. It stops at the first invalid line and reports its line number:
+
+```console
+$ printf '1000\n2048\n' | humanize naturalsize
+1.0 kB
+2.0 kB
+```
+
 ### Human-readable floating point numbers
 
 ```pycon
diff --git a/docs/filesize.md b/docs/filesize.md
index 9f3cf500..551c0f38 100644
--- a/docs/filesize.md
+++ b/docs/filesize.md
@@ -1,3 +1,26 @@
 # Filesize
 
 ::: humanize.filesize
+
+## Command line
+
+Format a byte count with the `humanize` command or with `python -m humanize`:
+
+```console
+$ humanize naturalsize 8589934592
+8.6 GB
+$ humanize naturalsize --binary 8589934592
+8.0 GiB
+$ humanize naturalsize --gnu --format "%.2f" 8589934592
+8.00G
+```
+
+With no positional value, one value is read from each input line:
+
+```console
+$ printf '1000\n2048\n' | humanize naturalsize
+1.0 kB
+2.0 kB
+```
+
+Invalid values produce an error identifying the input line and a nonzero exit status.
diff --git a/pyproject.toml b/pyproject.toml
index 63817fec..bb99921e 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -47,6 +47,7 @@ urls.Documentation = "https://humanize.readthedocs.io/"
 urls.Funding = "https://tidelift.com/subscription/pkg/pypi-humanize?utm_source=pypi-humanize&utm_medium=pypi"
 urls.Homepage = "https://github.com/python-humanize/humanize"
 urls.Source = "https://github.com/python-humanize/humanize"
+scripts.humanize = "humanize.cli:main"
 
 [tool.hatch]
 version.source = "vcs"
diff --git a/src/humanize/__main__.py b/src/humanize/__main__.py
new file mode 100644
index 00000000..295030a7
--- /dev/null
+++ b/src/humanize/__main__.py
@@ -0,0 +1,10 @@
+"""Run humanize as a module."""
+
+from __future__ import annotations
+
+import sys
+
+from humanize.cli import main
+
+if __name__ == "__main__":
+    sys.exit(main())
diff --git a/src/humanize/cli.py b/src/humanize/cli.py
new file mode 100644
index 00000000..b5aebd58
--- /dev/null
+++ b/src/humanize/cli.py
@@ -0,0 +1,93 @@
+"""Command-line interface for humanize."""
+
+from __future__ import annotations
+
+import argparse
+import sys
+from collections.abc import Iterable, Sequence
+from typing import TextIO
+
+from humanize.filesize import naturalsize
+
+
+def _parser() -> argparse.ArgumentParser:
+    parser = argparse.ArgumentParser(prog="humanize")
+    commands = parser.add_subparsers(dest="command", required=True)
+
+    filesize = commands.add_parser(
+        "naturalsize",
+        help="format byte counts as human-readable file sizes",
+        description="format byte counts as human-readable file sizes",
+    )
+    filesize.add_argument(
+        "value",
+        nargs="?",
+        help="number of bytes; read one value per line from stdin when omitted",
+    )
+    filesize.add_argument(
+        "--binary",
+        action="store_true",
+        help="use binary units such as KiB and MiB",
+    )
+    filesize.add_argument(
+        "--gnu",
+        action="store_true",
+        help="use GNU-style binary units such as K and M",
+    )
+    filesize.add_argument(
+        "--format",
+        default="%.1f",
+        help="format string for the numeric portion (default: %%.1f)",
+    )
+    return parser
+
+
+def _format_value(value: str, args: argparse.Namespace) -> str:
+    return naturalsize(value, binary=args.binary, gnu=args.gnu, format=args.format)
+
+
+def _run_naturalsize(
+    args: argparse.Namespace,
+    stdin: TextIO,
+    stdout: TextIO,
+    stderr: TextIO,
+) -> int:
+    try:
+        _format_value("1024", args)
+    except (TypeError, ValueError, OverflowError) as error:
+        stderr.write(f"humanize: error: invalid format {args.format!r}: {error}\n")
+        return 2
+
+    if args.value is not None:
+        values: Iterable[tuple[int, str]] = ((1, args.value),)
+    elif stdin.isatty():
+        stderr.write("humanize: error: a value is required when stdin is interactive\n")
+        return 2
+    else:
+        values = enumerate(stdin, start=1)
+
+    for line_number, value in values:
+        value = value.strip()
+        try:
+            result = _format_value(value, args)
+        except (TypeError, ValueError, OverflowError) as error:
+            if args.value is not None:
+                stderr.write(f"humanize: error: invalid value {value!r}: {error}\n")
+            else:
+                stderr.write(
+                    f"humanize: error: invalid value on line {line_number} "
+                    f"{value!r}: {error}\n"
+                )
+            return 2
+        stdout.write(result + "\n")
+
+    return 0
+
+
+def main(argv: Sequence[str] | None = None) -> int:
+    """Run the humanize command-line interface."""
+    args = _parser().parse_args(argv)
+    if args.command == "naturalsize":
+        return _run_naturalsize(args, sys.stdin, sys.stdout, sys.stderr)
+    command = f"unknown command: {args.command}"
+    raise AssertionError(command)
diff --git a/tests/test_cli.py b/tests/test_cli.py
new file mode 100644
index 00000000..1f0c1271
--- /dev/null
+++ b/tests/test_cli.py
@@ -0,0 +1,134 @@
+"""Tests for the humanize command-line interface."""
+
+from __future__ import annotations
+
+import io
+import os
+import subprocess
+import sys
+from pathlib import Path
+
+import pytest
+
+from humanize.cli import main
+
+ROOT = Path(__file__).parents[1]
+
+
+def run_cli(
+    args: list[str],
+    input_text: str = "",
+    *,
+    interactive: bool = False,
+) -> tuple[int, str, str]:
+    stdin = io.StringIO(input_text)
+    stdin.isatty = lambda: interactive  # type: ignore[method-assign]
+    stdout = io.StringIO()
+    stderr = io.StringIO()
+
+    old_stdin, old_stdout, old_stderr = sys.stdin, sys.stdout, sys.stderr
+    try:
+        sys.stdin, sys.stdout, sys.stderr = stdin, stdout, stderr
+        try:
+            status = main(args)
+        except SystemExit as error:
+            status = error.code if isinstance(error.code, int) else 1
+    finally:
+        sys.stdin, sys.stdout, sys.stderr = old_stdin, old_stdout, old_stderr
+    return status, stdout.getvalue(), stderr.getvalue()
+
+
+def test_naturalsize_defaults_to_decimal() -> None:
+    assert run_cli(["naturalsize", "8589934592"]) == (0, "8.6 GB\n", "")
+
+
+@pytest.mark.parametrize(
+    "option, expected",
+    [
+        ("--binary", "8.0 GiB\n"),
+        ("--gnu", "8.0G\n"),
+    ],
+)
+def test_naturalsize_supports_unit_options(option: str, expected: str) -> None:
+    assert run_cli(["naturalsize", option, "8589934592"]) == (0, expected, "")
+
+
+def test_naturalsize_supports_custom_format() -> None:
+    assert run_cli(["naturalsize", "--format", "%.2f", "3000"]) == (
+        0,
+        "3.00 kB\n",
+        "",
+    )
+
+
+def test_naturalsize_reads_one_value_per_piped_line() -> None:
+    assert run_cli(["naturalsize"], "1000\n2048\n") == (
+        0,
+        "1.0 kB\n2.0 kB\n",
+        "",
+    )
+
+
+def test_naturalsize_reports_invalid_piped_line() -> None:
+    assert run_cli(["naturalsize"], "1000\nnot-a-number\n3000\n") == (
+        2,
+        "1.0 kB\n",
+        (
+            "humanize: error: invalid value on line 2 'not-a-number': "
+            "could not convert string to float: 'not-a-number'\n"
+        ),
+    )
+
+
+def test_naturalsize_reports_invalid_value() -> None:
+    status, stdout, stderr = run_cli(["naturalsize", "invalid"])
+
+    assert status == 2
+    assert stdout == ""
+    assert "invalid value 'invalid'" in stderr
+    assert "could not convert string to float" in stderr
+
+
+def test_naturalsize_reports_malformed_format() -> None:
+    status, stdout, stderr = run_cli(["naturalsize", "--format", "%q", "3000"])
+
+    assert status == 2
+    assert stdout == ""
+    assert "invalid format '%q'" in stderr
+    assert "unsupported format character" in stderr
+
+
+def test_naturalsize_requires_value_for_interactive_stdin() -> None:
+    assert run_cli(["naturalsize"], interactive=True) == (
+        2,
+        "",
+        "humanize: error: a value is required when stdin is interactive\n",
+    )
+
+
+def test_help() -> None:
+    status, stdout, stderr = run_cli(["naturalsize", "--help"])
+
+    assert status == 0
+    assert "format byte counts as human-readable file sizes" in stdout
+    assert "--binary" in stdout
+    assert "--gnu" in stdout
+    assert "--format" in stdout
+    assert stderr == ""
+
+
+def test_python_module_invocation() -> None:
+    env = os.environ.copy()
+    env["PYTHONPATH"] = str(ROOT / "src")
+    result = subprocess.run(
+        [sys.executable, "-m", "humanize", "naturalsize", "8589934592"],
+        cwd=ROOT,
+        env=env,
+        capture_output=True,
+        text=True,
+        check=False,
+    )
+
+    assert result.returncode == 0
+    assert result.stdout == "8.6 GB\n"
+    assert result.stderr == ""