Convert Octal to Binary

Convert octal to binary instantly, e.g. chmod 755 into permission bits — free online.

About

About the Octal to Binary Converter

A Unix permission code like chmod 755 is really just octal shorthand for a string of permission bits — converting octal to binary expands each digit back into the 3 bits it represents, so you can see exactly which read, write and execute flags are set.

Each octal digit expands to exactly three bits, which is why chmod values decode so cleanly: 7 is 111 (read, write, execute), 5 is 101 (read and execute) and 4 is 100 (read only). 644 therefore becomes 110 100 100 — the owner can read and write, and everyone else can only read.

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Guide

Using the Octal to Binary Converter

  1. 1

    Step 1

    Octal is already selected below as the input base.

  2. 2

    Step 2

    Type your octal digits (0-7) into the value box.

  3. 3

    Step 3

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

  4. 4

    Step 4

    For a quick manual check, replace each octal digit with its 3-bit binary equivalent and string them together.

  • Expands octal into binary as you type
  • Rejects 8 and 9 immediately, since they aren't valid octal digits
  • Accepts an optional 0o prefix, as written in Python and JavaScript
  • 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 decode a chmod value into its read, write and execute bits.

Developers

Developers check what a umask such as 022 actually removes.

Security auditors

Auditors confirm which permission bits a file mode grants to group and others.

Students

Students check three-bits-per-digit expansions.

Popular base conversions

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

Examples

Octal to Binary examples

4 worked examples

01

chmod 755 permission

Octal 755 converts to binary 111101101 — read in groups of 3, that's the rwxr-xr-x permission bits.

02

A small octal value

Octal 17 converts to binary 1111, since 17 octal equals 15 in decimal.

03

A round octal number

Octal 100 converts to binary 1000000, since 100 octal equals 64 in decimal.

04

A regular file's permissions

644 converts to 110100100 — owner read-write, everyone else read-only.

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FAQ

Frequently asked questions

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

How do I convert octal to binary?

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

How do you convert octal to binary by hand?

Replace each octal digit with its 3-bit binary form and concatenate them: 755 becomes 111, 101 and 101, giving 111101101.

What does chmod 755 mean in binary?

755 in octal expands to 111101101 in binary — read in groups of 3 as rwx (111) for the owner, r-x (101) for the group, and r-x (101) for everyone else.

Is this octal to binary converter free?

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

Can I convert binary back to octal?

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

How large an octal value 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.

Can I enter octal with a leading 0 or 0o?

Yes. A 0o prefix is stripped and a plain leading 0 doesn't change the value, so 0o644, 0644 and 644 all give 110100100.

Why is an 8 or 9 rejected?

Octal only uses the digits 0 to 7, so an 8 or 9 means the number isn't octal. Instead of guessing, the tool shows a message listing the digits it accepts.

What do the bits of chmod 644 mean?

110 100 100 reads as rw- r-- r--: the owner can read and write, while the group and everyone else can only read.

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