What is a Factorial Calculator?
The factorial of a number n, written n!, is the product of all whole numbers from 1 to n. For example, 5! = 5 x 4 x 3 x 2 x 1 = 120. Factorials grow extremely fast, so most calculators give up and show a rounded value. This one shows the full exact number.
When to use it
Use it for permutations and combinations, probability homework, algorithm complexity checks, or just to see how big 100! or 1000! really is. By convention, 0! equals 1.
How it works
The tool multiplies the numbers together using arbitrary-precision integers (BigInt), so there is no floating-point rounding. That means the answer is every digit of the true result, however long. Very large inputs take a moment and produce very long numbers.
Frequently asked questions
What is 0 factorial?
0! is defined as 1. This keeps formulas for permutations and combinations consistent.
How big is 100 factorial?
100! has 158 digits. It starts with 9332621544... and ends with 24 zeros.
Can I calculate the factorial of a negative number or a decimal?
Not with the standard definition. Factorials are defined for whole numbers 0 and above. Decimals need the gamma function, which this tool does not use.
Why does my phone calculator show a scientific notation value?
Most calculators use floating-point numbers, which lose exactness. This tool shows every digit.