Octal to decimal converter

Type an octal number, like 755 or 0o755, and the decimal appears straight away, with each digit's place value worked out underneath. Octal digits go from 0 to 7, so an 8 or 9 is flagged. Several numbers can go in at once, separated by spaces, commas or new lines.

Each place in an octal number is worth 8 times the place to its right, so the places are 1, 8, 64, 512 and so on. Multiply each digit by its place value and add them up.

For 755, the 7 is in the 64s place, the first 5 in the 8s place and the last 5 in the ones place. That's 7 × 64 + 5 × 8 + 5 × 1 = 448 + 40 + 5 = 493.

Octal was common on early computers whose words were multiples of 3 bits. Today it's mostly seen in Unix file permissions, where each digit is three bits, for read, write and run. In chmod 755, the 7 (111) gives the owner all three and each 5 (101) gives read and run. The chmod calculator spells it out.