About this tool
Enter n and r to compute the number of permutations (nPr, where order matters) and combinations (nCr, where it does not). It uses exact BigInt arithmetic so even large counts stay precise — all in your browser.
Frequently asked questions
What is the difference between nPr and nCr?
nPr counts ordered arrangements of r items chosen from n, while nCr counts unordered selections. nCr always equals nPr divided by r factorial.
Why must r be at most n?
You cannot choose more items than are available, so r must be between 0 and n. Larger r values are rejected with a notice.