Factorial Calculator
Calculate the factorial of a number.
Multiplying down to one
The factorial of a number is the product of all the whole numbers from it down to one — five factorial is five times four times three times two times one, which is 120. This calculates factorials, which appear throughout counting and probability.
Enter a number to calculate its factorial.
Why factorials explode
Factorials count the number of ways to arrange a set of items in order — five items can be arranged in five factorial, or 120, different sequences — which is why they are the foundation of permutations and probability. The striking thing about factorials is how fast they grow: they outpace even exponential growth, so the factorial of a modest number is already enormous, and it does not take a large input before the result exceeds what most calculators can display. This explosive growth is exactly why the number of possible arrangements of even a small deck of cards is astronomically large. Factorials capture, in one operation, just how quickly the possibilities multiply when order matters.
Common questions
What does a factorial count?
The number of ways to arrange a set of items in order — five items can be ordered in five factorial, which is 120, different ways.
Why do factorials grow so fast?
Each step multiplies by a larger number, so they outpace even exponential growth — the factorial of a modest number is already enormous.
Is anything uploaded?
No. The calculation happens in your browser.