Octal Addition Calculator

How it is calculated

Each field takes a whole octal number made only of the digits 0 to 7, with no sign, space, point or prefix; a digit 8 or 9, or an empty field, gives no result, and leading zeros are accepted and ignored. The tool converts both numbers to decimal (value = Σ digit × 8position), adds them, and converts the sum back to octal. It shows four results: the octal sum, the decimal sum and the decimal value of each input, so you can check the work. When adding by hand, go column by column from the right and carry 1 whenever a column reaches 8, because 8 is written 10 in octal. Each number may have up to 17 octal digits once leading zeros are removed; a longer number shows no result rather than rounded digits.

Common mistakes

• Typing the digit 8 or 9. These do not exist in octal, so the calculator returns nothing; 8 is written 10.
• Carrying at 10 instead of at 8, as in decimal. In octal 7 + 1 is 10, not 8, and 7 + 7 is 16 (one eight and six).
• Reading the octal sum as a decimal number. 1041 here means 545 in decimal, and the decimal line is the one to use for ordinary arithmetic.
• Entering a minus sign, a decimal point or a prefix such as 0o. Only plain digits 0 to 7 are accepted.
• Pasting a number longer than 17 octal digits. The tool refuses it instead of rounding, so use a big-integer tool for such values.