Number Converters · Browser · Free

Decimal to Octal Converter

Type a decimal number and read off its octal form, with the binary and hexadecimal forms shown alongside.

What this tool does

Decimal is base 10 and octal is base 8, so the same amount ends up written with a different string of digits. One text field takes the number you want changed. A minus sign in front is accepted, a fractional point inside is accepted, and several numbers separated by spaces are converted one by one. Beside the octal answer the tool also shows the binary form and the hexadecimal form, and any letters there print in uppercase.

Nothing is worked out beforehand: the form computes only when you press Convert. The result then appears in a card below the button. Copy writes that result and its unit to the clipboard, and Clear resets the form so you can start on a fresh number.

Decimal to octal formula

Octal counts in groups of eight. The right-hand digit stands for single units, the digit to its left stands for groups of eight, and the next digit to the left stands for groups of sixty-four. The octal digits 144 therefore mean one group of sixty-four, four groups of eight and four single units, which is the decimal number 100 listed in the table below. The table shows the same place value on its own line as well: 64 in decimal is written 100 in octal.

To work the other way by hand, divide the decimal number by 8 and set the remainder aside, then divide what is left by 8 again, and keep going until nothing remains. Reading those remainders from the last one back to the first gives the octal digits. For 100 that trail of remainders is 4, 4 and 1, which spells the 144 the table gives, and larger rows follow the same shape: 255 becomes 377 and 1024 becomes 2000.