Octal Converter

About Octal converter

Converts whole numbers between octal and decimal, binary or hexadecimal, using six ready-made conversion types chosen with radio buttons. Octal is the number system behind Unix file permissions, and each digit lines up with exactly three binary bits.

How to use it

1. The page opens with Decimal to Octal selected. Choose a different one of the six options under Conversion Type, such as Octal to Binary, if you need another direction.
2. Type the number into the input, whose label changes to match the source system.
3. Press Convert.
4. Copy the answer from the Result field using the copy button attached to it.

A typical permission mode

755 with Octal to Binary selected

111101101 (which is 493 in decimal)

When to use it

• Translating a chmod value such as 644 into the individual read and write bits it stands for.
• Reading octal escape sequences found in old C source or printf output.
• Converting a decimal permission mask into the octal form a script expects.
• Practicing base conversion for a computer architecture course.

Questions about Octal converter

Why does 755 in binary look like a permission pattern?

Each octal digit expands to three bits: 7 is 111, 5 is 101. Read as owner, group and others, those bits mean read-write-execute, then read and execute twice.

Can I include a leading zero or a 0o prefix?

Yes. Leading zeros are fine, since 0755 is read as 755, and the marker that belongs to the source system is stripped: 0o for octal, 0x for hexadecimal and 0b for binary. Spaces and underscores between digits are ignored too.

What gets rejected?

Any digit that does not exist in the source system, such as an 8 in octal or a 2 in binary, produces a message naming the base and the digits it allows. Decimal points and other symbols are refused the same way.

Can it handle negative or very large numbers?

Both. A leading minus sign is carried through as a minus sign, not a two's complement pattern. The arithmetic is exact, so 22 sevens in octal converts to 73786976294838206463 in decimal with no rounding.

Does this convert text?

No, this page only handles numbers written in the four systems. Use the ASCII converter to see the decimal character codes of letters.

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