All Tools VerseConvert Hex to Octal
Convert hex to octal (base 8) with BigInt precision. Prefix toggle (none/0/0o), digit grouping, optional Unix permissions helper. Free, offline, 100% client-side.
- Runs in your browser
- Nothing uploaded
- Free, no sign-up
Convert hexadecimal to octal (base 8) using BigInt - handles 64-bit, 128-bit, and arbitrarily large values without Number precision loss. Pick prefix style (0 C / 0o Python), optional digit grouping, and a Unix file-permission helper for 3- or 4-digit octal values.
How to Use Convert Hex to Octal
- Paste your hex values, one per line. The
0x/0Xprefix is optional; spaces, underscores, and newlines are stripped automatically. Case-insensitive. - Pick an output prefix: None for bare octal (as used by
chmod),0for C/C++ style (0755), or0ofor Python 3 / ES6 / Rust literal form (0o755). - Toggle digit grouping to get
33 653 337 357instead of33653337357- purely visual, underlying value unchanged. - Enable "Show Unix permissions" if your hex values represent 3-digit (or 4-digit with sticky/setuid) file modes. The breakdown then adds a
rwxr-xr-x-style line for each applicable row. - Press Convert (or Ctrl+Enter / Cmd+Enter). Auto-convert fires 200 ms after each keystroke so results appear as you type.
- Read the stats line: total lines, successes, failures, and the largest decimal value in the batch.
- Inspect the breakdown: each row shows hex → decimal → octal chain, plus the binary form and optional Unix mode.
Frequently Asked Questions
How does hex-to-octal conversion work?
The tool reads the hex as a BigInt and emits it in base 8. Each group of 3 binary bits (formed from the underlying value) becomes one octal digit. Hex 0xFF is 8 bits = 11111111, which regroups from the right as 011 111 111 = 377 octal. The pipeline is hex → BigInt → base-8 string.
Does this really support BigInt for huge hex values?
Yes – JavaScript’s native BigInt, verified. A 16-digit hex like 0xFFFFFFFFFFFFFFFF (264 − 1) converts to the exact octal string 1777777777777777777777. Earlier versions of this page used parseInt(hex, 16) which silently rounds any 14+ digit hex past 253; that’s been fixed.
What’s the difference between the 3 prefix modes?
None gives bare digits (e.g. 755), the format used by Unix chmod. 0 prepends a zero (0755), the traditional C and PHP literal form – but also ambiguous with leading-zero decimals in some contexts, which is why it’s deprecated in modern JavaScript. 0o prepends 0o (0o755), the unambiguous modern form used in Python 3, ES6 JavaScript, and Rust.
What does the Unix permissions helper do?
When enabled, and the octal value is exactly 3 or 4 digits, the breakdown adds a symbolic mode line: 755 → rwxr-xr-x, 644 → rw-r--r--, 1755 → rwxr-xr-t (sticky bit), 4755 → rwsr-xr-x (setuid), 2755 → rwxr-sr-x (setgid). Values with different digit counts are skipped.
Which hex input formats are accepted?
Bare hex digits (FF), C-style prefix (0xFF/0XFF), space-separated (DE AD BE EF), underscore-separated (DE_AD_BE_EF), or any mix across multiple lines. Case-insensitive – aB and AB decode identically.
Why would I want octal output?
Three main use cases in 2026: Unix file permissions (chmod 755 is canonical); microcontroller datasheets that still specify register values in octal; and compact binary display for 9-bit or 12-bit fields where hex would waste space. Older PDP-11/VMS code still uses it too.
What happens if one line has a bad character?
Only that line fails. The tool processes lines independently, so a stray Z in one row becomes a single red entry in the breakdown (“Line 3: invalid hex character ‘Z’ at position 2”) while every other line still converts. Copy and Download capture only the good output.
Is my data uploaded anywhere?
No. All arithmetic runs in your browser’s JavaScript engine – no network requests fire during conversion, no server stores or logs your hex values. You can verify with your browser’s Network tab. The tool works offline after the initial page load.
How do I go from octal back to hex?
Use our “octal to hex” converter, or in code: parseInt('755', 8).toString(16) in JavaScript ('1ed'), or hex(0o755) in Python. Both directions are lossless for any value.
What’s the biggest hex value this can handle?
There’s no practical upper bound. BigInt is arbitrary-precision, so a 1,024-digit hex value converts to its exact octal representation. Performance is O(n) in digit count – 10,000 lines of 64-bit hex finish under 100 ms on a modern laptop.
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