Convert Decimal to Octal

Convert decimal numbers to octal (base 8) instantly — free online converter.

About

About the Decimal to Octal Converter

Octal numbers still turn up in Unix permission codes and in C-style literals that start with a leading zero, so converting decimal to octal is mostly about translating a familiar everyday number into that older base-8 notation.

Repeated division works here too, dividing by 8 instead of 2: 493 ÷ 8 = 61 r 5, 61 ÷ 8 = 7 r 5, and 7 ÷ 8 = 0 r 7, so 493 is 755 in octal. That's exactly the permission number chmod 755 uses, one of the few places you'll still meet octal in everyday work.

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Guide

Using the Decimal to Octal Converter

  1. 1

    Step 1

    Decimal is already selected below as the input base.

  2. 2

    Step 2

    Type your ordinary base-10 number into the value box.

  3. 3

    Step 3

    The result table fills in instantly — the octal value sits alongside binary, decimal and hex all at once.

  4. 4

    Step 4

    For a quick manual check, divide the number by 8 repeatedly, writing down each remainder, then read the remainders back from bottom to top.

  • Converts decimal to octal as you type, using only the digits 0–7
  • Shows the result without a leading 0 or 0o, so you can add whichever prefix your language expects
  • Handles negative numbers with a leading minus sign
  • 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

Linux administrators

Admins check that a file mode printed as a decimal number, like 493, really is chmod 755.

C and Python developers

Developers write an octal literal correctly — 0755 in C, 0o755 in Python.

Students

Students check divide-by-8 conversions from coursework.

Anyone reading old documentation

Readers of older manuals and file-format specs convert values into the octal they're listed in.

Popular base conversions

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

Examples

Decimal to Octal examples

3 worked examples

01

A chmod value

493 in decimal equals 755 in octal — the number behind the common Unix chmod 755 permission.

02

Classroom example

64 in decimal equals 100 in octal.

03

Ten in octal

10 converts to 12 in octal — one group of eight plus two.

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FAQ

Frequently asked questions

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

How do I convert decimal to octal?

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

How do you convert decimal to octal by hand?

Divide the number by 8 repeatedly and keep each remainder: 493 ÷ 8 = 61 remainder 5, 61 ÷ 8 = 7 remainder 5, 7 ÷ 8 = 0 remainder 7. Reading the remainders bottom to top gives 755.

What is 493 in octal?

493 in decimal is 755 in octal — the same number behind the common Unix chmod 755 permission setting (read/write/execute for the owner, read/execute for everyone else).

Is this decimal to octal converter free?

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

Can I convert octal back to decimal?

Yes — the same converter works in both directions. Select octal as the input base instead, or use the dedicated octal to decimal converter page.

How large a decimal number can I convert?

Up to 9,007,199,254,740,991 — beyond that the conversion won't be exact, and the tool will tell you so.

Why does chmod use octal instead of decimal?

Each octal digit holds exactly three bits — read, write and execute — so one digit describes one group of users. The same permissions written in decimal, 493 for 755, hide that structure completely.

Can I enter a negative number or a fraction?

Negative whole numbers work and keep their minus sign, so -8 becomes -10. Fractions such as 8.5 aren't accepted — the tool converts whole numbers only.

Where else is octal used today?

Mainly in Unix file permissions and in some escape sequences, such as \101 for the letter A in C strings. Hex has replaced octal almost everywhere else, because it maps more neatly onto 8-bit bytes.

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