Convert Octal to Hexadecimal

Convert octal to hexadecimal instantly — free online octal to hex number converter.

About

About the Octal to Hexadecimal Converter

Octal and hex describe the same bits in two different groupings, so converting octal to hex mostly comes up when older base-8 notation — a legacy permission code or escape sequence — needs to be lined up against the hex form used everywhere else in modern code.

Going from octal to hex means regrouping the same bits from threes into fours. Octal 377 is 011 111 111; drop the leading zero and regroup from the right as 1111 1111, and you get FF — the largest value one byte can hold. That's why the escape \377 in a C or shell string is the same byte a hex editor shows as FF.

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Guide

Using the Octal to Hexadecimal 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 hex value sits alongside binary, decimal and octal all at once.

  4. 4

    Step 4

    For a quick manual check, expand each octal digit to 3 bits, then regroup the whole binary string into groups of 4 bits from the right to read off the hex digits.

  • Converts octal to hex as you type, with uppercase A–F in the result
  • Accepts an optional 0o prefix and rejects 8 and 9 as invalid digits
  • Shows binary alongside, so you can see the three-to-four bit regrouping
  • 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

Developers modernising code

Developers rewrite octal constants from legacy code as hex.

Reverse engineers

Reverse engineers match octal escapes like \377 to the hex byte FF in a dump.

Embedded developers

Developers translate octal values from older datasheets into the hex their compiler and debugger use.

Students

Students check conversions between the two bases via binary.

Popular base conversions

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

Examples

Octal to Hexadecimal examples

4 worked examples

01

chmod 755 permission

Octal 755 converts to hex 1ED, since 755 octal equals 493 in decimal.

02

A small octal value

Octal 17 converts to hex F, since 17 octal equals 15 in decimal.

03

A round octal number

Octal 100 converts to hex 40, since 100 octal equals 64 in decimal.

04

Permissions 644

644 converts to 1A4 in hex.

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FAQ

Frequently asked questions

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

How do I convert octal to hex?

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

How do you convert octal to hex by hand?

There's no direct digit-for-digit shortcut between octal and hex, since 8 and 16 don't group the same bits evenly — expand the octal to binary first, then regroup the binary into 4-bit chunks to read off the hex digits.

Why isn't there a quick octal-to-hex shortcut like there is for octal-to-binary?

Octal digits map cleanly to groups of 3 bits and hex digits to groups of 4 bits, but 3 and 4 don't share a common grouping — so converting between them means going through binary (or decimal) as a middle step.

Is this octal to hex converter free?

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

Can I convert hex back to octal?

Yes — the same converter works in both directions. Select hexadecimal as the input base instead, or use the dedicated hex 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 0o prefix?

Yes. The 0o is stripped before converting, so 0o777 and 777 both give 1FF.

What is chmod 644 in hex?

1A4. Octal 644 is 420 in decimal, which is 1A4 in hexadecimal.

Why are the digits 8 and 9 not allowed?

Octal has only the digits 0 to 7. A value containing 8 or 9 isn't octal, so the tool asks you to check the input instead of converting it.

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