Decimal to Octal Converter

Octal is base 8, a number system that uses only the digits 0 through 7. Each position is worth eight times the one to its right, so octal 100 equals 64 in decimal. Everyday decimal is base 10 and uses digits 0 through 9.

The most common place is Unix and Linux file permissions, where modes like 755 and 644 are octal. Octal also appears in older computing systems, some hardware registers, and as a compact way to read binary three bits at a time.

Repeatedly divide the decimal number by 8 and note each remainder. Reading the remainders from last to first gives the octal value. For example 64 divided by 8 is 8 remainder 0, then 8 divided by 8 is 1 remainder 0, so 64 becomes 100.

Those are the decimal forms of common file permission modes. 420 in octal is 644, which is read and write for the owner and read for others, while 493 is 755, adding execute rights. Chmod writes them in octal, but scripts sometimes store the decimal.

No practical limit. The converter uses arbitrary-precision BigInt maths, so numbers with hundreds of digits convert to the exact octal value with no floating-point rounding error.

Yes. Commas and spaces are stripped before converting, so grouped input like 1,000 or 4 096 gives the same result as the plain digits. Any other non-digit character is rejected as invalid.

No. Only non-negative whole numbers are supported. A minus sign, a decimal point or letters will show an Invalid number message, since octal here represents integers exactly rather than fractions.

The output simply stays blank. Nothing is calculated until there is at least one digit to convert, and clearing the input clears the result too.

No. The conversion runs entirely in your browser using local JavaScript, so the numbers you enter never leave your device or get logged.