Factorial calculator
Calculator
The calculator needs JavaScript. The tables below give the same numbers for common cases.
How it is worked out
- 10! = 10 × 9 × 8 × 7 × 6 × 5 × 4 × 3 × … × 1.
- By definition 0! = 1.
| Inputs | Answer |
|---|---|
| n: 5 | 5! = 120. |
| n: 10 | 10! = 3,628,800. |
| n: 20 | 20! = 2,432,902,008,176,640,000. |
| n: 0 | 0! = 1. |
How to use it
The factorial of n, written n!, is the product of all whole numbers from 1 to n: 5! = 5 × 4 × 3 × 2 × 1 = 120. By definition 0! = 1.
Factorials count the ways to arrange n different things in a row and appear in permutation and combination formulas. They grow very fast: 20! is already about 2.4 × 10¹⁸, and 170! is the largest that fits an ordinary floating-point number.
Frequently asked questions
What is 10 factorial?
10! = 3,628,800.
Why is 0! equal to 1?
There is exactly one way to arrange nothing, and the definition keeps the permutation and combination formulas consistent.
How many ways can 5 people line up?
5! = 120.
Method: standard arithmetic shown step by step; no outside data is used. Checked 2026-11-12.
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General information only. Results are plain arithmetic on the numbers you enter; check anything important (money, health, school work) against your own records or the official source.