What is octal used for?

Octal is commonly used for Unix/Linux file permissions (e.g. chmod 755), legacy systems, and some network protocols. Each octal digit represents exactly 3 binary bits.

Does it accept the 0o prefix?

Yes. Both '755' and '0o755' are accepted as octal inputs.

How does octal map to chmod permissions?

Each octal digit is three bits: read (4), write (2) and execute (1). 755 is 111 101 101 in binary, which is rwxr-xr-x; the chmod calculator shows the symbolic form directly.

Why do 8 and 9 show an error?

Octal digits run from 0 to 7. Typing 8 or 9 shows Not a valid OCT value. Allowed digits: 0-7. until you remove it.

Octal converter

Enter an octal number (base 8, digits 0–7) to see its decimal, binary, and hexadecimal equivalents. Useful for Unix file permissions and legacy systems.

OCT input (base 8)

BIN–

OCT–

DEC–

HEX–

INPUT BASE

All bases shown simultaneously.

Runs entirely in your browser

Worked example

755 = 7×64 + 5×8 + 5 = 493 in decimal. Each octal digit is three bits, so 755 is 111 101 101: the rwxr-xr-x permission set.

How it works

The input is checked digit by digit and turned into a JavaScript BigInt, then written out with BigInt.prototype.toString(base), so large values stay exact. All four bases are computed simultaneously from the same input value, so you can see binary, octal, decimal, and hex at a glance.

Processing runs in your browser

All conversion runs in your browser tab. Our servers are not involved at any point.

Related operations

For converting between data sizes like KB and MB, try the byte converter. To compute MD5 or SHA hashes from values, use the hash generator. For working with file permission bits, see the chmod calculator.

Frequently asked questions

What is octal used for?: Octal is commonly used for Unix/Linux file permissions (e.g. chmod 755), legacy systems, and some network protocols. Each octal digit represents exactly 3 binary bits.
Does it accept the 0o prefix?: Yes. Both '755' and '0o755' are accepted as octal inputs.
How does octal map to chmod permissions?: Each octal digit is three bits: read (4), write (2) and execute (1). 755 is 111 101 101 in binary, which is rwxr-xr-x; the chmod calculator shows the symbolic form directly.
Why do 8 and 9 show an error?: Octal digits run from 0 to 7. Typing 8 or 9 shows Not a valid OCT value. Allowed digits: 0-7. until you remove it.

Last reviewed September 30, 2026

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