Frequently Asked Questions
Everything you need to know about the Permutation & Combination Calculator.
What's the difference between a permutation and a combination?
A permutation counts arrangements where order matters; a combination counts selections where order doesn't matter.
How is nPr calculated?
Using n! / (n−r)!, the number of ordered ways to choose r items from n.
How is nCr calculated?
Using n! / (r!(n−r)!), the number of unordered ways to choose r items from n.
What does "with repetition" mean?
It allows the same item to be chosen more than once, which changes the formula (n^r for permutations, (n+r−1)Cr for combinations).
What if r is greater than n?
Without repetition that's impossible (you can't choose more items than exist), so the calculator flags it as invalid rather than returning zero silently.
Can it handle large numbers like 20!?
Yes, exact arithmetic is used so large factorials remain precise; extremely large results switch to scientific notation for display.
Does it show the factorial working?
Yes, the formula is shown fully substituted with your n and r values, including the computed factorials.
Can n or r be zero?
Yes, both are valid: 0! = 1, so results involving zero are handled correctly (e.g. nC0 = 1).
Is my data stored?
No, everything runs client-side in your browser.
Is it free?
Yes, completely free with no sign-up or limits.