The factorial n! is the product of every whole number from n down to 1, so 5! = 5 × 4 × 3 × 2 × 1 = 120. By definition 0! = 1, and factorials are only defined for non-negative integers.

How accurate is the result for large n?

Results are exact, not approximate. The calculator uses JavaScript BigInt arbitrary-precision arithmetic, so even huge factorials are computed digit-for-digit. A cap keeps the browser responsive on extreme inputs.

Is my input sent anywhere?

No. The calculator is privacy-first — n stays in your browser and nothing is transmitted to any server.

Why is 0! equal to 1?

There is exactly one way to arrange zero objects (the empty arrangement), so 0! = 1 by convention. It also keeps formulas like nCr = n! / (r!(n−r)!) consistent for edge cases.

How big can the factorial get here?

The exact BigInt path is capped at 5000! to keep the browser responsive. Even at that cap the result has over 16,000 digits, all computed digit-for-digit with no rounding.

What are factorials used for?

Factorials count permutations and underpin combinations, probability, the binomial theorem, Taylor series and many statistics formulas. n! is the number of distinct orderings of n items.

Can I compute the factorial of a negative number or a decimal?

No. The factorial is only defined for non-negative integers. Generalisations to other numbers use the gamma function, which this calculator does not compute.

Factorial Calculator (n!)

Factorial calculator

The factorial of a number, written n!, is the product of every whole number from n down to 1. It is one of the most common building blocks in combinatorics — counting permutations, combinations and arrangements — and it appears in probability, calculus (Taylor series) and statistics. This calculator returns the exact value of n! for any non-negative integer, not a rounded approximation, and shows how many digits the answer has.

How it works

The tool multiplies n × (n−1) × (n−2) × … × 2 × 1 using JavaScript’s BigInt type, which supports arbitrary-precision integers. Because ordinary floating-point numbers lose precision above 2^53, BigInt is essential for large factorials — it stores every digit exactly. By definition 0! = 1. To keep the browser responsive the exact path is capped at 5000!, and the digit count is displayed alongside the result.

Example

For n = 10: 10! = 10 × 9 × 8 × 7 × 6 × 5 × 4 × 3 × 2 × 1 = 3,628,800 (7 digits). This is the number of different ways to order 10 distinct items.

n	n!	Digits
0	1	1
5	120	3
10	3,628,800	7
13	6,227,020,800	10
20	2,432,902,008,176,640,000	19

Everything runs locally in your browser — the number you enter never leaves your device.