Combination Calculator — nCr (n Choose r)

Count unordered selections nCr—poker hands, committees, and lottery lines where {A,B,C} equals {C,B,A}.

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nCr counts unordered selections: how many ways to choose r items from n when order does not matter. 52C5 = 2,598,960 distinct five-card poker hands from a standard deck.

10C3 = 120

By Muhammad Abdullah Rauf · Founder, EverydayTools.proUpdated 2026-07-03· Reviewed by EverydayTools Editorial Team

What does nCr count?

Combinations count groups, not sequences. A committee of three from ten people has the same members whether Alice is listed first or third—only the set {Alice, Bob, Carol} matters.

Formula: nCr = n! / (r! × (n−r)!) — often read “n choose r.” The extra r! in the denominator strips the r! ways to reorder each subset that permutations would treat as different.

**Relationship:** nCr = nPr / r!. If 5P3 = 60 ordered triples, dividing by 3! = 6 gives 5C3 = 10 unordered triples.

Pascal's triangle rows list binomial coefficients C(n,k). Row n sums to 2^n—the number of subsets of an n-element set. Combinations appear in probability whenever drawing without order: lottery balls, committees, card hands.

Order ignored → nCr. Enter n and r for exact “n choose r,” then use probability calculator for event fractions.

Quick answers

Concise answers for common searches — definitions, steps, and comparisons.

What is 52 choose 5?

52C5 = 2,598,960 distinct five-card hands from a standard 52-card deck.

How do you convert nPr to nCr?

Divide by r!: nCr = nPr / r!. Example: 5P3/3! = 60/6 = 10 = 5C3.

What is 10 choose 3?

10C3 = 120 unordered triples from ten distinct items.

Why is nC0 always 1?

There is exactly one way to choose nothing—the empty subset.

Combination formula

Computes nCr via exact factorial ratios with BigInt cancellation, avoiding overflow from computing n! alone.

Formula

nCr = n! / (r! (n−r)!) for 0 ≤ r ≤ n. Pascal rule: C(n,k) = C(n−1,k−1) + C(n−1,k). Binomial theorem: (x+y)^n = Σ C(n,k) x^k y^(n−k).

Assumptions

  • Items are distinct and selection is without replacement.
  • Order within the chosen group does not matter.

Limitations

  • Does not model combinations with repetition (stars and bars)—different formula C(n+r−1, r).
  • Identical objects in the pool need multiset coefficients, not raw nCr.

How to use Combination Calculator — nCr (n Choose r)

  1. Verify order is irrelevant

    If listing {1,2,3} is the same as {3,2,1}, combinations apply. Ranked awards need permutations.

  2. Enter n and r

    Pool size n; subset size r with 0 ≤ r ≤ n.

  3. Use symmetry when helpful

    nC(n−r) equals nCr—choosing 2 to leave out of 10 matches choosing 8 to keep.

  4. Feed into probability

    Favorable combinations ÷ total nCr gives probability when outcomes are equally likely.

Combination Calculator — nCr (n Choose r) examples

Intro pair

Input

n = 5, r = 2

Output

5C2 = 10

Ten unordered pairs from five elements.

Committee of three

Input

n = 10, r = 3

Output

10C3 = 120

120 teams of three—order of names on the roster ignored.

Symmetry trick

Input

n = 20, r = 18

Output

20C18 = 20C2 = 190

Choosing 18 to include equals choosing 2 to exclude.

Poker anchor

Input

n = 52, r = 5

Output

52C5 = 2,598,960

Standard five-card hand count from full deck.

Edge cases

Input

n = 7, r = 0 and r = 7

Output

7C0 = 7C7 = 1

Empty set and full set each have exactly one combination.

Link from permutation

Input

5P3 = 60

Output

5C3 = 60/6 = 10

Divide ordered count by 3! to drop order.

When to use a combination calculator

Common real-world scenarios where this tool saves time.

Poker or card hands

Five cards from 52: 52C5 = 2,598,960 possible hands—denominator for flush probabilities.

Lottery ticket space

Pick 6 numbers from 49: 49C6 ≈ 13.98 million combinations—odds math starts here.

Hiring or jury selection

Choose 4 finalists from 20 applicants where rank within the group is irrelevant: 20C4.

Quality sampling

Inspect 5 units from a batch of 100 without caring about inspection order: 100C5 sample sets.

Workflow guides

Step-by-step chains that connect related tools for common tasks.

Related mathematical concepts

  1. Permutations nPr overcount each combination by r! reorderings.
  2. Binomial coefficients C(n,k) expand (a+b)^n and model coin-flip counts.
  3. Hypergeometric probability uses combinations when drawing without replacement from finite pools.
  4. Multinomial coefficients generalize nCr when splitting into more than two labeled groups.

Reference tables

nCr values for small n

n \ r01234
414641
51510105
616152015
717213535

Pascal's triangle rows—each entry sums to 2^n.

Lottery-style combination counts

PoolPicknCrOrder of magnitude
49613,983,816~14 million
5955,006,386~5 million
90557,958,470~58 million

Best practices

Cancel factorials before multiplying

Compute 100C3 as (100×99×98)/(3×2×1) to avoid 100! entirely.

Use Pascal's triangle for small n

Row 6: 1,6,15,20,15,6,1—quick lookup for n ≤ 10 on exams.

Pair with probability calculator

Once favorable and total combinations are known, probability is their ratio.

Check nCr ≤ nPr

Combinations never exceed permutations for the same n,r—catches mode errors.

Common mistakes to avoid

Using nPr for unordered committees

Divide nPr by r! or use nCr directly—otherwise you overcount by every reordering.

Double-counting symmetric pairs

nCr already counts each subset once. Do not divide by 2 again for pairs unless problem defines labeled ends.

Confusing with combinations with repetition

Choosing 3 fruits from {apple, banana, cherry} allowing duplicates uses stars-and-bars, not nCr.

Treating suited cards as identical

Standard 52C5 treats cards as distinct—even same rank different suits are different items.

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Frequently Asked Questions

What is the difference between 10C3 and 10P3?

10C3 = 120 ignores order. 10P3 = 720 counts every ordering—720/6 = 120.

Can nCr be computed when n − r is smaller than r?

Yes—use symmetry nCr = nC(n−r) to multiply fewer terms.

How do combinations appear in binomial probability?

Exactly k successes in n trials has C(n,k) × p^k × (1−p)^(n−k) favorable patterns.

Is choosing a president and treasurer a combination?

No—roles are ordered. Use permutations or multiply combinations by r! for labeled positions.

What is combination with replacement?

Also called multiset combinations—formula C(n+r−1, r), not standard nCr.

Why divide by (n−r)! in the formula?

n!/(n−r)! is nPr; dividing by r! removes order. Together they count subsets only.

How large can nCr grow?

Peaks near r = n/2. 100C50 has 30 digits—use exact tools, not floating calculators.

Privacy, accuracy, and trust

Privacy

Combination inputs are calculated locally without server upload.

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Reviewed by EverydayTools Editorial Team on 2026-07-03.

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