# Combination Calculator

> Calculate C(n, r) for unordered selections, using the multiplicative form for stability across small and large inputs.

**URL:** https://www.calculatoranswers.com/combination-calculator
**Category:** Education

## Quick Answer

Calculate the number of unique groups of items where order does not matter. Enter the total items and choice size.

## Definition

A combination calculator computes the number of unique ways to select a subset of items from a larger set where the order of selection does not matter. Using the combination formula C(n, r) = n! / (r! * (n-r)!), the tool utilizes stable multiplicative algorithms to prevent arithmetic overflow on large inputs. It also supports combinations with repetition allowed. Researchers, game developers, and math students use this tool to calculate lottery odds, schedule tournament matchups, and analyze statistical subsets.

## How to Use

1. **Choose selection mode** — Select whether item repetition is allowed in the combinations.
2. **Enter pool size (n)** — Type the total number of unique items available in the pool.
3. **Enter sample size (r)** — Input the number of items to select for each group.
4. **Read combinations count** — View the calculated number of unique combinations with the step-by-step factorial work.

## Disclaimer

This calculator provides estimates for educational and planning purposes. Always consult a qualified professional for specific advice on financial, medical, legal, or other regulated decisions.

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