Factorial Calculator

Calculate factorials (n!) with full multiplication chains and Stirling's approximation for large numbers.

Calculate n!

Enter any whole number 0–170

N (Integer)

! =

Digits

Stirling Approx

Multiplication Chain

Factorial Table (0! to 20!)

Formulas

Factorial Definition

n! = n × (n−1) × ... × 2 × 1

Stirling's Approximation

n! ≈ √(2πn) × (n/e)ⁿ

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Pro Tips

By convention, 0! = 1. This makes many formulas work correctly.

Factorials grow extremely fast. 20! already has 19 digits!

Factorials are used in permutations (nPr = n!/(n−r)!) and combinations (nCr = n!/(r!(n−r)!)).