Hex to Octal Converter

Convert hexadecimal (base 16) numbers to octal (base 8).

Uppercase output (0–7 only, but consistent with hex casing)

Hexadecimal (one number per line, optional 0x prefix)

Octal

377
5274
764
17777777777
20

Hex to octal conversion explained

Hexadecimal (base 16) groups four binary bits per digit while octal (base 8) uses three. The simplest path from hex to octal goes through binary: expand each hex digit to four bits, then regroup into threes — so ff → 11111111 → 377. This tool skips the intermediate steps and converts directly using BigInt arithmetic. For the reverse, use the Octal to Hex Converter. You can also jump to Hex to Decimal or the full Base Converter.

Built and maintained by Meet Shah · Last updated 1 August 2026

What this tool is used for

Converting a hex value into the octal form a legacy tool or a permission field expects.
Checking a hex constant against an octal one in a header file that defines both.
Converting a hex escape into an octal escape for another language.
Reading a hex value against documentation written in octal.
Working through a conversion between two non-decimal bases.

Frequently Asked Questions

Why go through binary to convert hex to octal by hand?: Because 16 and 8 are both powers of two but not of each other: a hex digit is 4 bits and an octal digit is 3, so they never line up. Expanding to bits and regrouping in threes is the shortcut — ff becomes 11111111 becomes 377 — and it needs no division at any point.
Does the output have uppercase and lowercase forms?: No, and that is the point of the difference between the two bases. Octal uses only the digits 0–7, so there are no letters to change case — unlike hex, where a–f can be written either way and tools disagree about which to emit.
How large can the numbers be?: Unbounded. Each line is parsed with BigInt, so a 64-digit hex value converts exactly. Going through a JavaScript number instead would start silently rounding above 2⁵³ − 1 — about 13 hex digits — which is well within the range of a real memory address or hash fragment.
Is the 0x prefix required?: No, it is stripped if present and ignored if absent, so both 0xff and ff work. The prefix carries no information here — it exists in source code to tell a compiler which base a literal is in, and this tool has already been told.
Why does octal survive at all in modern computing?: Almost entirely for Unix file permissions, where three bits map exactly onto read, write and execute — which is why chmod 755 is octal and reads naturally as rwx, r-x, r-x. Outside permissions and a few legacy formats, hex has replaced it because bytes divide evenly into two hex digits and not into octal ones.

Common errors and gotchas

Converting digit by digit, which fails because four bits per hex digit does not divide into three.
Losing the width, so leading zeros disappear and the bit alignment changes.
Assuming a fixed digit ratio between the two bases, which depends on the value.
Dropping or adding a prefix that the destination treats as significant.
Producing an octal value longer than the target field accepts and having it truncated.