Octal to Decimal Converter

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Convert an octal number to decimal. Each octal digit (0–7) is multiplied by a power of 8 and summed, so 755 in octal becomes 7·64 + 5·8 + 5 = 493 in decimal. The most common reason to do this conversion today is to interpret Unix file permissions: chmod 755 means a permissions value of 493, and chmod 644 means 420. Octal also still appears in C-style integer literals beginning with a leading zero.

Octal (8)

Allowed: 0–7

Decimal (10)

Allowed: 0–9

Octal (8) → Decimal (10)

Quick reference table

Octal (8)Decimal (10)
77
108
10064
644420
755493
777511
77774095

Glossary

Octal (base 8)

The octal numeral system uses digits 0 through 7. It was popular in early computing because each octal digit maps cleanly to exactly three binary digits, which made it convenient for systems with 12-, 24- or 36-bit words. Today its most common surviving use is Unix file permissions: chmod 755 means owner-rwx, group-rx, others-rx, where each digit is a 3-bit permission mask.

Decimal (base 10)

The decimal numeral system is the everyday number system used by humans, with digits 0 through 9. Each digit position represents a power of 10 — units, tens, hundreds, thousands. It is sometimes called base-10 or denary. All four bases on this page convert through decimal as a canonical integer value, so a round-trip such as binary → decimal → hex always produces the exact same number.

Related tools

Decimal to Octal
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Octal to Hex
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