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Wheel Probability Calculator

Enter the number of segments and spins to see the spin odds.

Result

8.33%
0.83 hits
58.11%

How it is calculated

With n equal segments and s spins, for one chosen segment: P(each spin) = 1 ÷ n × 100, expected hits = s ÷ n and P(at least one hit) = (1 − (1 − 1/n)s) × 100. The number of segments is rounded to the nearest whole number (12.6 is treated as 13) and must be at least 1. Spins must be zero or more; 0 spins gives 0% for the at-least-one result. All segments are assumed equally likely and every spin independent of the last, so a weighted or biased wheel will not match. Results are shown to two decimals; the maths is the same in every country.

Worked example

A wheel with 12 segments spun 10 times, looking for one particular prize segment. Per spin: 1 ÷ 12 = 8.33%. Expected hits: 10 ÷ 12 = 0.83. Chance of missing on every spin: (11/12)10 ≈ 0.4189, so at least one hit is 1 − 0.4189 = 58.11%. Ten spins are therefore not even a guarantee of landing on it once.

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Common mistakes

  • Believing the odds add up: 10 spins at 8.33% are not 83.3% for at least one hit. The chance per spin never changes, and misses compound, giving 58.11%.
  • Reading expected hits of 0.83 as a promise of one win; it is an average over many repeated sessions of 10 spins.
  • Treating a gap of several misses as making the segment due. Each spin is independent, so the next spin is still 8.33%.
  • Entering a prize that covers several segments as one segment; count the winning slices and multiply the per-spin odds by that number, or use the combined count.
  • Using the tool for wheels with unequal slices or a weighted wheel, which this equal-segment formula cannot represent.

About this calculator

For a wheel divided into equal segments — a prize wheel, roulette-style spinner, or raffle wheel — the probability of landing on any single segment on one spin is simply 1 divided by the number of segments. But predicting outcomes over many spins requires binomial probability: the expected number of hits equals the per-spin probability times the number of spins, while the chance of landing on a target segment at least once uses the complement rule, 1 minus the probability of missing it every single time.

This calculator applies both formulas to a wheel with a given number of segments and spins, returning the per-spin odds, expected hits, and at-least-one-hit probability. It's useful for game designers balancing prize-wheel odds, streamers and promoters running wheel-spin giveaways, and students working through basic probability and binomial distribution problems who want a concrete, spin-based example to check their own calculations against.

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Comments (1)

  • Editorial team

    To size a promotion, run the tool backwards. Keep the segment count fixed and raise the number of spins until the at-least-one figure reaches your target. On an 8 segment wheel, 17 spins give 89.67% and 18 spins give 90.96%, so 18 is the first count that clears 90% for one chosen segment. What hit chance do you design your own wheel or giveaway around?

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