Factorial Calculator
Compute n!, permutations and combinations exactly.
How to use
- 1 Choose factorial, permutations, or combinations.
- 2 Enter n, and r as well for nPr or nCr.
- 3 Read the exact result and its digit count.
- 4 Copy the full value to use elsewhere.
About Factorial Calculator
The Factorial Calculator computes three closely related counting quantities exactly: the factorial of a number, the number of permutations (nPr), and the number of combinations (nCr).
Because these values grow astronomically — 20! already has nineteen digits — the tool uses big-integer arithmetic throughout and returns the full result as a string, with no rounding or scientific-notation approximation.
A factorial, written n!, is the product of every whole number from one up to n, and it is the foundation of combinatorics.
Permutations count the ordered ways to choose r items from n; combinations count the unordered ways.
These appear whenever you are working out probabilities, arranging or selecting items, or sizing a problem — how many lottery tickets, how many seating orders, how many ways to pick a committee.
Doing this on an ordinary calculator quickly overflows into imprecise floating point, so the digits stop being trustworthy.
This tool computes nPr and nCr multiplicatively to keep the intermediate numbers manageable and the final answer exact, and caps n at ten thousand so the page stays responsive.
You see the full number and its digit count, and a copy button puts the exact value on your clipboard.
It all runs locally in your browser.
FAQ
How large a factorial can it handle?
It computes n! exactly for n up to 10,000 using big-integer arithmetic, returning the complete number rather than an approximation.
What is the difference between nPr and nCr?
Permutations (nPr) count ordered selections of r items from n; combinations (nCr) count unordered selections, where order does not matter.
Why is the result shown as a string?
Values this large exceed the range of ordinary numbers, so the exact result is returned as text to preserve every digit.