How do I convert octal to decimal?

Multiply each digit by 8 raised to its position, counting from 0 on the right, and add the results.

Why does it say my number is invalid?

Octal uses only the digits 0 to 7. A digit 8 or 9 is not allowed.

Can I convert several numbers at once?

Yes. Paste them into the list box, one per line.

Octal to Decimal Converter: Convert Base 8 to Base 10 with Steps

Enter an octal number and get its decimal value, with each digit and its place value shown.

The method

Each octal digit is worth a power of 8, starting from 8 to the power 0 on the right. Multiply each digit by its place value and add the results.

755 in octal
7 x 64 = 448
5 x  8 =  40
5 x  1 =   5
Total  = 493

So octal 755 is 493 in decimal.

Reading the working table

For each digit, the table shows its position, the power of 8 for that position, and the digit multiplied by that power. The sum of the last column is your answer. Very long numbers are converted exactly, and the table shows the first 40 digits.

Valid input

Octal numbers contain only the digits 0 to 7. If you type an 8 or 9, the tool tells you which character is wrong. Prefixes such as 0o and leading zeros are accepted.

Common values

10 in octal is 8
17 in octal is 15
144 in octal is 100
377 in octal is 255
777 in octal is 511

Octal 777 is the familiar full-permission file mode. For the other direction, use decimal to octal. To see binary as well, try octal to binary, or the octal converter.

Octal to Decimal Converter

Working

Quick reference

The method

Reading the working table

Valid input

Common values

Frequently asked questions