How to use the Permutation and Combination Calculator
This tool counts ordered arrangements (permutations) and unordered selections (combinations).
Open the Permutation and Combination Calculator →
What you need to enter
- n (total items)
- r (chosen items)
The formula
nPr = n! ÷ (n − r)!. nCr = n! ÷ (r!(n − r)!).
Worked example
Using the default values in the calculator:
- n (total items): 10
- r (chosen items): 3
| Combinations nCr | 120 |
| Permutations nPr | 720 |
| n! | 3,628,800 |
Tips for better results
- Order matters for permutations only.
- Large factorials use exact big numbers.
Common mistakes to avoid
- Mixing up nPr and nCr.
- r larger than n.