Factorial Calculator
Factorial Calculator works out Result and Exact value from n and Function. The default figures on this page give result of 3,628,800; change any entry and the result, the working and the sources update together.
Your figures
Updates as you typeHow this is worked out
2 steps
- 10! multiplies every whole number from 10 down to 1.
- Trailing zeros come from factors of 10 = 2 x 5, and fives are scarcer: floor(10/5) + floor(10/25) + ... = 2.
Its 5 worked examples are re-run on every release, last on 15 September 2026. What changed
Sources and references
3 sources
What the Factorial Calculator calculates
Computes n! exactly with arbitrary-precision integers, plus the double factorial n!!, the subfactorial !n (derangements), the gamma function extension to non-integers, digit counts and trailing zeros.
How to use this Factorial Calculator
Enter n and Function. Result updates as you type, and “Use a worked example” loads checked figures you can adjust. Change one figure at a time to see what drives the result.
How the result is worked out
Open “How this is worked out” beside the result for the step-by-step calculation behind Result, Exact value and Number of digits.
The method follows NIST Digital Library of Mathematical Functions, 5.2 Gamma Function Definitions and 5.4 Special Values, NIST DLMF 26.13 and OEIS A000166 (subfactorial / derangement recurrence D(n) = nD(n-1) + (-1)^n) and Legendre's formula for the exponent of a prime in n! (Hardy & Wright, An Introduction to the Theory of Numbers, Theorem 416).
10 factorial example
With n: 10, Function: factorial, the calculator returns Result: 3628800, Exact value: 3628800, Trailing zeros: 2. This example is checked against an independent source in the test suite.
What you can compare
Change one input at a time to see how it affects Result, Exact value and Number of digits. The inputs you can vary are n and Function.
Results are general information, not financial, tax, legal, medical or engineering advice. Check any decision that matters with a qualified professional.
See something wrong? Report a problem with this calculator
Frequently asked questions
How to do factorial on a calculator?
Computes n! Open “How this is worked out” beside the result to see each step for your own figures.
How to do factorial on TI-84?
It needs n and Function. Nothing else is required, and the figures stay in your browser.
Where is factorial on a Casio calculator?
Computes n! On the figures this page opens with — n 10 — the result is 3,628,800. Put your own figures in their place and the working updates beside the result.
Is there an easy way to calculate factorials?
The result gives Result, Exact value, Number of digits, log10 of the result, Natural log of the result and Scientific notation, each labelled with its unit so the figure can be read on its own.
What information do I need for the Factorial Calculator?
You need n and Function. The page opens with default figures that give result of 3,628,800, so you can see the scale before entering your own.
What does this Factorial Calculator show?
It shows Result, Exact value, Number of digits, log10 of the result, Natural log of the result, Scientific notation, Expanded product and Trailing zeros, with the working and any warnings for your entries.