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Octal to Decimal
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Decimal · base 10
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Hexadecimal · base 16
Binary · base 2
Octal · base 8
Enter a octal value above to convert it
// about this tool

Octal to Decimal Online

Updated 2026-10-24

Convert octal to decimal online for free. Paste an octal value and SnapTools shows its decimal (base-10) value instantly, right in your browser. Nothing you enter is uploaded.

Octal notation is most familiar from Unix file permissions (chmod 755), but some tools and APIs expect that same value as a plain base-10 integer instead. This converter runs the base-8 positional arithmetic for you, multiplying each digit by the right power of 8, so you get the exact decimal equivalent without doing it by hand. For every base at once, use the Number Base Converter.

// how to use

  1. 1 Paste or type an octal (base-8) value into the input, using digits 0-7 only.
  2. 2 SnapTools converts it to decimal as you type.
  3. 3 Copy the decimal result, or open the Number Base Converter for all bases at once.

// examples

Common file permission
Input
755
Output
493
Byte value
Input
377
Output
255

// common uses

Converting a Unix permission value (chmod 755) into its plain integer form Reading legacy octal literals from C or POSIX code as ordinary numbers Checking a manual octal-to-decimal conversion Learning base-8 positional notation

// faq

Is octal notation a modern invention created for computing?
No. In 1718, the Swedish philosopher Emanuel Swedenborg proposed a full octal counting system at the request of King Charles XII, arguing base 8 was more "geometrical" than base 10 because it can be halved repeatedly down to 1. Computing revived the idea two centuries later since it maps cleanly onto 3-bit groups.
How do I convert octal to decimal by hand?
Positional value is the trick here. The rightmost digit counts once, the next counts eight times as much, the one after that sixty-four times, and so on, so you multiply and add across the digits. For 755, that comes to 7 lots of 64 plus 5 lots of 8 plus 5 lots of 1, totaling 493.
Why would I want a permission value like 755 in decimal?
Some APIs and file-metadata tools store or report Unix permission bits as a plain integer rather than the usual octal notation, so converting a familiar chmod value to decimal is a common lookup.
Does it accept a leading 0 (like old-style octal literals)?
That leading zero carries no extra meaning in octal, it is just padding, so this tool ignores it automatically rather than requiring the string to be trimmed first.
What if my input has an 8 or 9 in it?
An 8 or a 9 simply is not a valid octal digit, so encountering one in the input trips the validation check, and you are asked to fix it before a decimal answer gets produced.

// works with your data

Decimal to Octal Octal to Hex Octal to Binary Number Base Converter Hex to Decimal Hash Identifier

Use this via API

Get a free API key → 
curl -X POST https://thesnaptools.com/api/v1/tools/octal-to-decimal \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"number":"755"}'