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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 2026-10-24

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, using 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

Why did early JavaScript treat a number like 010 as octal instead of decimal?
Early JavaScript treated any number literal starting with a leading zero as octal, so 010 silently evaluated to 8, not ten. The confusion this caused was significant enough that ECMAScript 5, in 2009, deprecated the behavior in favor of an explicit 0o prefix for real octal values.
How do I convert octal to binary by hand?
Look up the 3-bit pattern for each octal digit on its own (7 is 111, 5 is 101, 0 is 000) and line those patterns up left to right in the same order as the original digits. This tool handles the lookup and strips redundant leading zeros automatically.
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 and 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?
Since base 8 has no use for the digits 8 or 9, the tool treats either one as invalid input and flags it right away instead of guessing at a 3-bit group that does not really exist.

// works with your data

Binary to Octal Octal to Hex Octal to Decimal Number Base Converter Hex to Binary Word Frequency Counter

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"}'