About the Long Multiplication Calculator
Long multiplication is the written method taught in school for multiplying numbers too big to do in your head. This calculator shows the full working: one partial product for each digit of the second number, with the place-value zeros added, and then the rows added together. It handles decimals by multiplying the digits and putting the point back at the end, and it uses exact whole-number arithmetic so even very long numbers come out right, digit for digit. Use it to check homework or to see where a calculation went wrong.
Updated October 2026
How to use the Long Multiplication Calculator
- 1Type the first number.
- 2Type the number to multiply by.
- 3Read the answer.
- 4Follow the working laid out in columns.
- 5Read the numbered steps underneath to see what each row means.
The method step by step
Write the larger number on top and the smaller underneath, lining up the right-hand digits. Multiply the top number by the ones digit and write the result. Move to the tens digit, write a zero in the ones column first, and multiply again. Carry on for every digit, then draw a line and add the rows.
A full worked example
Here is 347 × 28 the way the calculator lays it out.
- 347 × 8 = 2,776 (the ones row)
- 347 × 2 = 694, written as 6,940 (the tens row)
- 2,776 + 6,940 = 9,716
Checking your answer
Round both numbers and multiply in your head: 350 × 30 = 10,500, so 9,716 is in the right area. You can also check the last digit: 7 × 8 = 56 ends in 6, and so does 9,716. If your own working disagrees with the calculator, compare it row by row to find the slip, which is usually a forgotten carry or a missing zero.
Why learn the written method
Calculators give answers, but written multiplication builds number sense and is still expected in exams. It also generalises: the same steps work for multiplying polynomials in algebra.
Multiplying very large numbers
Ordinary calculators switch to scientific notation once a product passes about 15 digits and quietly drop the last digits. This tool keeps every digit, so 123,456,789,123,456,789 × 987,654,321 comes out exactly. That is useful for checking cryptography exercises, factorial-style puzzles and anything where the final digits matter.
Using it on a phone
The working is shown in a fixed-width font so the columns line up, and it scrolls sideways if the numbers are very long. The steps are the same on paper, and other written methods follow them. Divide with the Long Division Calculator, add the partial products with the Long Addition Calculator, and handle very long numbers with the Big Number Calculator.
Features
- Partial products shown row by row
- Place-value zeros explained
- Decimals handled correctly
- Exact answers for very long numbers
- Negative numbers supported
- Copy the answer
Frequently asked questions
How do you do long multiplication?
Multiply the top number by each digit of the bottom number, starting from the ones. Shift each new row one place left by adding a zero, then add all the rows. 347 × 28 = 2,776 + 6,940 = 9,716.
Why do we add zeros in long multiplication?
Because each digit further left is worth ten times more. The 2 in 28 means 20, so 347 × 20 is written as 347 × 2 with a zero on the end.
How do I multiply decimals with long multiplication?
Ignore the points, multiply the whole numbers, then count the digits after the points in both numbers and put the point that many places from the right. 3.25 × 1.4: 325 × 14 = 4,550, three decimal places, so 4.550 = 4.55.
Is this the same as the grid method?
The answer is the same. The grid method splits numbers into tens and ones in a table; long multiplication writes one row per digit. Many schools teach both.
How big can the numbers be?
Up to 60 digits each. The calculator uses exact arithmetic, so there are no rounding errors.
What about negative numbers?
Multiply as normal and make the answer negative if exactly one of the numbers is negative.