How long multiplication works
- Write the two numbers stacked, with the longer one on top.
- Multiply the top number by each digit of the bottom number, one digit at a time, starting from the units.
- Each new partial product is shifted one place to the left of the previous one (because each digit's place value is 10× bigger).
- Add all the partial products to get the final answer.
a × (bn·10n + … + b1·10 + b0) = a·bn·10n + … + a·b1·10 + a·b0
FAQ
Does this support negatives or decimals?
Negatives are supported — the sign of the product follows the standard sign rules. For decimals, multiply as if both were whole numbers and shift the decimal point by the total number of decimal places at the end (or use the big number calculator).
Why are some rows shorter than others?
If a digit of the bottom number is 0 the partial product is 0, which is sometimes written as a single 0 with the appropriate shift. The calculator displays the row to make the position visible.