Factorial, Permutations & Combinations Calculator
Compute n!, nPr and nCr exactly for any size of number — runs 100% in your browser with no upload.
120
20
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🔒 Calculated in your browser — nothing is uploaded. Exact BigInt math keeps even huge results precise.
What this calculator does
Enter a total count n and a chosen count r, and this tool instantly returns three answers: the factorial n! (the product of every whole number from 1 up to n), the number of permutations nPr (how many ordered arrangements of r items you can pick from n), and the number of combinations nCr (how many unordered selections of r items you can pick from n). Order matters for permutations but not for combinations, so nPr is always at least as large as nCr. Every result updates live as you type.
Why exact big-number math matters
Factorials grow astonishingly fast — 20! already exceeds two quintillion — so ordinary floating-point numbers quietly lose precision and start returning rounded, wrong digits. This calculator uses JavaScript BigInt arithmetic, which stores integers of unlimited size, so the full exact value is shown as a string with every digit intact. That makes it reliable for probability, statistics, lottery and card-hand odds, combinatorics homework, and anywhere a single wrong digit would matter.
Frequently asked questions
What is the difference between nPr and nCr?
Both count how many ways you can pick r items from a group of n. Permutations (nPr) count arrangements where order matters, so ABC and CBA are different. Combinations (nCr) count selections where order does not matter, so ABC and CBA are the same. That is why nPr is always greater than or equal to nCr.
Can it handle very large factorials without rounding?
Yes. The tool uses BigInt integer math, so results are exact to the last digit no matter how many digits they have — unlike scientific-notation calculators that round large factorials.
Is anything I enter uploaded to a server?
No. Every calculation runs entirely in your browser using JavaScript. The numbers you type are never sent, stored, or logged anywhere.