# Combinations Calculator (nCr)

> Combinations calculator (nCr): find how many ways you can choose r items from n, with the combination formula explained step by step. Free, no signup.

- **Canonical URL:** https://boringtoolskit.com/combinations-calculator/
- **Category:** Everyday Calculators
- **Evidence level:** authored-methodology
- **Reviewed:** July 26, 2026
- **Last verified:** 2026-10-12
- **Privacy:** Inputs and results stay in this browser unless the page clearly labels an external request.

## How it works

C(n, r) = n! / (r! x (n - r)!).

## Worked example

Choosing 3 items from 10 gives C(10, 3) = 120 distinct combinations.

## Assumptions

- Order does not matter; for ordered selections use permutations.
- n and r are whole numbers with 0 <= r <= n.

## Related tools

- /permutation-calculator/
- /probability-calculator/
- /factorial-calculator/

## Sources

- [Calculation methodology](/methodology/)
- [Quality evidence and verification standard](/quality-evidence/)

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