Convert Binary to Octal

Convert binary to octal instantly, handy for Unix chmod permissions — free online.

About

About the Binary to Octal Converter

Octal groups binary digits three at a time, which is why it still shows up in Unix file permissions like chmod 755 — converting binary to octal makes those permission bits easier to read at a glance than a long string of 0s and 1s.

Octal works in groups of three bits, because 8 is 2³: 111 101 101 becomes 7, 5 and 5 — the familiar 755. Splitting from the right and padding the leftmost group with zeros is the manual method; the converter does the same thing instantly and shows decimal and hex alongside, so you can cross-check any permission or flag value.

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Guide

Using the Binary to Octal Converter

  1. 1

    Step 1

    Binary is already selected below as the input base.

  2. 2

    Step 2

    Type or paste your binary digits (0s and 1s) into the value box.

  3. 3

    Step 3

    The result table fills in instantly — the octal value sits alongside hex, decimal and binary all at once.

  4. 4

    Step 4

    For a quick manual check, split the binary into groups of 3 bits from the right and convert each group to a single octal digit (0-7).

  • Converts binary to octal as you type, grouping the bits in threes for you
  • Handles 9-bit permission masks and much longer bit strings alike, up to 53 bits
  • Shows decimal and hex next to the octal result for a quick cross-check
  • Shows the value in binary, octal, decimal, hexadecimal and base 36 at once, plus any custom base from 2 to 36
  • Exact for whole numbers up to 9,007,199,254,740,991, and tells you when a number is too large
  • Runs entirely in your browser — free, with no sign-up and no limit

Linux administrators

Admins turn a set of rwx bits such as 111101101 into the chmod value 755.

Students

Students check three-bit grouping exercises without redoing them by hand.

Embedded developers

Developers read octal-encoded fields in older protocols and file formats.

Retro-computing fans

Hobbyists working with octal-based machines like the PDP-8 translate bit patterns into front-panel octal.

Popular base conversions

Binary Decimal Binary Hexadecimal Octal Binary Octal Decimal Octal Hexadecimal Decimal Binary Decimal Octal Decimal Hexadecimal Hexadecimal Binary Hexadecimal Octal Hexadecimal Decimal

Examples

Binary to Octal examples

4 worked examples

01

Unix permission bits

111101101 in binary equals 755 in octal — the classic chmod 755 permission, split into three 3-bit groups.

02

Classroom example

1010 in binary equals 12 in octal.

03

A full byte

11111111 in binary equals 377 in octal.

04

Permission bits for 644

110100100 converts to 644, the usual permission for a regular file: owner read-write, everyone else read-only.

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FAQ

Frequently asked questions

Quick answers to common questions about the Binary to Octal Converter.

How do I convert binary to octal?

Type your binary number above, with binary selected as the input base. The octal value appears instantly in the results table — nothing is uploaded anywhere.

How do you convert binary to octal by hand?

Split the binary digits into groups of 3, starting from the right (pad the leftmost group with zeros if needed), then convert each group of 3 bits to one octal digit: 111 101 101 becomes 755, for example.

Why is octal tied to Unix permissions?

Each Unix permission triad (read, write, execute) is exactly 3 bits, and 3 bits map to a single octal digit 0-7 — so chmod 755 is really the binary 111 101 101 written more compactly.

Is this binary to octal converter free?

Yes. It's free, with no sign-up and no limit on how many numbers you convert.

Can I convert octal back to binary?

Yes — the same converter works in both directions. Select octal as the input base instead, or use the dedicated octal to binary converter page.

How large a binary number can I convert?

Up to 9,007,199,254,740,991 in decimal terms — beyond that the conversion won't be exact, and the tool will tell you so.

Why group binary digits in threes for octal?

Each octal digit stands for exactly three bits, so you can convert one group at a time from the right: 110 101 101 is 6, 5 and 5, which gives octal 655.

Can I enter binary with a 0b prefix?

Yes. A leading 0b is removed before converting, so 0b111101101 and 111101101 both give 755.

Does the octal result include a 0 or 0o prefix?

No, you get the plain octal digits, such as 755. Add whatever prefix your language expects — 0o755 in Python and JavaScript, or 0755 in C — when you use it in code.

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