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Octal to Binary
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Decimal · base 10
Hexadecimal · base 16
Binary · base 2
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Octal · base 8
Enter a octal value above to convert it
// about this tool

Octal to Binary Online

Updated 2026-07-26

Convert octal to binary online for free. Paste an octal value and SnapTools shows its binary representation instantly, right in your browser. Nothing you enter is uploaded.

Because one octal digit is exactly three binary bits, octal is a compact way to write binary in groups of three — which is exactly why Unix permissions use it: 755 splits cleanly into three 3-bit permission groups, one each for owner, group, and other. This converter expands any octal value back to its raw bits in one step, so you can read a permission mask, check a manual conversion, or learn the mapping without doing the regrouping by hand. For every base at once, use the Number Base Converter.

// how to use

  1. 1 Paste or type an octal (base-8) value into the input — digits 0-7 only.
  2. 2 SnapTools converts it to binary as you type.
  3. 3 Copy the binary result, or open the Number Base Converter for all bases at once.

// examples

Common file permission
Input
755
Output
111101101
Byte value
Input
377
Output
11111111

// common uses

Reading a Unix permission value (chmod 755) as its individual permission bits Understanding how octal digits map to binary groups Debugging low-level data that uses octal notation Checking a manual octal-to-binary conversion

// faq

Is my input uploaded to a server?
No. The conversion runs entirely in your browser, so nothing you enter leaves your machine.
How do I convert octal to binary by hand?
Replace each octal digit with its exact 3-bit binary group — 7 is 111, 5 is 101, 0 is 000 — then concatenate them in order. This tool does it instantly and drops any leading zeros on the whole value.
Why is octal a shorthand for binary?
One octal digit maps to exactly three binary bits, the same relationship hex has with four bits. Octal was common on systems with word sizes divisible by 3 and lives on today mainly in Unix file permissions.
What does chmod 755 actually mean in binary?
755 breaks into three permission groups (owner/group/other) of 3 bits each — rwx for the owner, r-x for group and other — which is exactly why permissions are written in octal rather than decimal.
What if my input has an 8 or 9 in it?
Octal only uses digits 0-7. An 8 or 9 is flagged as invalid, since it cannot represent a real octal digit.

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Use this via API

Get a free API key → 
curl -X POST https://thesnaptools.com/api/v1/tools/octal-to-binary \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"number":"755"}'
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