Factorial Calculator (n!)
Exact factorials of any non-negative whole number from 0 to 1000, using big-integer arithmetic.
Reviewed by the WorldCalcs team · Methodology · Last reviewed: June 2026
5!
120
What is a factorial?
The factorial of a non-negative whole number n, written n!, is the product of every whole number from 1 up to n. So 5! = 5 × 4 × 3 × 2 × 1 = 120. By definition 0! = 1. Factorials count how many ways a set of things can be arranged in order, which makes them central to permutations, combinations and probability.
How it's calculated
Multiply all the whole numbers from 1 to n together: n! = n × (n − 1) × (n − 2) × ... × 2 × 1. Each factorial builds on the one before it, since n! = n × (n − 1)!. The values grow extremely fast, so exact results for larger inputs need big-integer arithmetic.
Example
To find 5!, multiply 5 × 4 × 3 × 2 × 1. Working left to right: 5 × 4 = 20, then × 3 = 60, then × 2 = 120, then × 1 = 120. So 5! = 120.
All calculations happen in your browser. Nothing is sent, stored, or tracked.
Results are estimates and may contain errors — for general information only, not professional advice. Always verify before relying on them. Disclaimer
How to use
Enter a non-negative whole number n. The calculator multiplies every whole number from 1 to n, using big-integer arithmetic so even large results are exact.
Results above 170! exceed standard floating-point precision — that is why this tool uses BigInt under the hood.