Wheel Spin Odds: How Slice Size and Weights Change the Chance of Winning
Most people use a wheel without thinking about the odds, and that is fine. But when there is a prize, or when you want to make a wheel favour some entries, a little arithmetic helps. This guide shows how to work out the percentage chance for each slice, how to weight an entry and how repeated spins change the picture.
On a fair wheel, the chance of landing on a slice is its share of the whole wheel. Ten equal slices give each a 10% chance. If you add one entry three times, it has three slices out of the total, so its chance is three times larger. Over several spins, the chance of winning at least once is 1 minus the chance of never winning.
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The basic rule
On a wheel where every slice is the same size, every entry has the same chance. Divide 100 by the number of slices to get the percentage.
| Slices | Chance per slice |
|---|---|
| 2 | 50% |
| 4 | 25% |
| 5 | 20% |
| 8 | 12.5% |
| 10 | 10% |
| 20 | 5% |
A wheel does not remember. If a slice came up last time, its chance this time is unchanged. This is the point people find hardest to accept, and it is the reason a name can appear twice in a row on a fair wheel.
Weighting an entry
To make one entry more likely, add it more than once. On the spinning wheel, type the same name on several lines. Every line is one slice, so three lines for the same name means three slices.
Here is a worked example with a prize wheel of 10 slices: one grand prize, three small prizes and six "try again" slices. The grand prize has a 1 in 10 chance, which is 10%. A small prize has 3 slices out of 10, so 30% to land on one of them. "Try again" has 60%.
- 1 grand prize = 10%
- 3 small prizes = 30%
- 6 try again = 60%
If you want the grand prize to be rarer, add more "try again" slices. With 19 "try again" slices and the same other slices, the grand prize drops to 1 in 23, about 4.3%. The prize wheel page is a good place to build a set like this.
The chance of winning at least once
If you spin more than once, work out the chance of never winning, then subtract it from 1. For a 10% prize and three spins, the chance of never winning is 0.9 times 0.9 times 0.9, which is 0.729. So the chance of winning at least once is about 27%, not 30%. People often add the chances together, which overstates the result.
| Spins | Chance of at least one 10% win |
|---|---|
| 1 | 10% |
| 3 | 27% |
| 5 | 41% |
| 10 | 65% |
| 20 | 88% |
Removing winners changes the odds
If you remove each winner after the spin, the odds for the rest improve each time. Start with ten equal slices at 10% each. After one is removed, nine slices remain at about 11.1% each. This is useful for classroom turns, because it guarantees that everyone is picked once.
A note on fairness
If you run a giveaway with a wheel, make sure everyone knows how the slices were set up. Showing the entry list before the spin, and keeping a screenshot afterwards, is the simplest way to keep trust. Our guide to running a fair giveaway covers the rest.
Frequently asked questions
What is the chance of landing on a slice?
It equals the slice's share of the wheel. One slice out of ten is 10%, and two slices out of ten is 20%.
How do I make one entry more likely?
Add it more than once. Each copy is another slice, so the entry's chance rises in proportion.
Does a slice that just won have a lower chance next time?
No. On a fair wheel every spin is independent. Use the remove-winner option if you want no repeats.
How do I work out the chance of winning in several spins?
Subtract the chance of losing every spin from 1. For a 10% chance over 5 spins, 1 minus 0.9 to the power of 5 is about 41%.