How to use the Factorial Calculator
- Enter a whole number n.
- Read n!, its number of digits and trailing zeros.
- Copy the full value if you need every digit.
What does this tool do?
The factorial n! is the product of every whole number from 1 to n: 5! = 5 × 4 × 3 × 2 × 1 = 120. By definition 0! = 1. Factorials count arrangements — n! is the number of ways to order n different items.
Factorials grow incredibly fast: 20! already exceeds 2 quintillion and 100! has 158 digits. The calculator uses exact big-integer arithmetic, so every digit is correct.
Why use it?
- Exact — no rounding, even for huge results.
- Counts digits and trailing zeros.
- Instant, in your browser.
The formula
n! = n × (n − 1) × … × 2 × 1
0! = 1
Privacy
The calculation happens instantly in your browser. The numbers you enter are not sent to our servers or saved. There's no account to create and nothing to install.
Frequently asked questions
Why does n! end in so many zeros?
Each pair of factors 2 and 5 produces a trailing zero. There are always more 2s than 5s, so the count of 5s decides it.
Last reviewed by the M2Toolkit team.