# Octal to Decimal Converter

> Convert octal numbers to decimal, binary and hexadecimal.

To convert octal to decimal, enter a base-8 value above using digits 0 to 7. Octal is still used for Unix file permissions, where each digit encodes read, write and execute bits for one class of user.

**URL:** https://convertto.tech/t/octal-to-decimal
**Category:** Number Tools (https://convertto.tech/c/number-tools)
**Privacy:** Runs entirely in the browser; no upload
**Cost:** Free, no sign-up
**Last updated:** 2026-08-01

## Key facts

- **Privacy:** Runs entirely in your browser — nothing is uploaded
- **Cost:** Free, unlimited, no sign-up

## How to use

1. Enter or paste your value.
2. The result appears immediately — copy or download it.

## FAQ

### Where is octal still used?

Unix file permissions, almost exclusively. chmod 755 is octal because each digit encodes exactly three permission bits — read, write and execute — which is the one place base 8 aligns neatly with the underlying data.

### Why does a leading zero change a number in some languages?

Because C and its descendants historically treated a leading zero as an octal prefix, so 010 meant 8. It is a notorious source of bugs in date handling, and modern languages either removed it or require an explicit 0o prefix.

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