Weighted Wheel Calculator

A weighted wheel is a probability distribution drawn as a circle, and the two have to agree: the chances must sum to one and the slices must fill 360 degrees with no gap. This turns your weights into both, shows the expected number of wins over however many spins you like, and checks that the arcs meet end to end.

Segments

One per line as "label, weight". Weights are relative, so doubling them all changes nothing.

Spins to expect over

Used only for the expected-wins column; it does not affect the odds.

Your result will appear here.

What this generator does

Divides each segment's weight by the total to get its probability, converts that to a slice angle, and lays the slices end to end around the circle. The probabilities, the angles and the expected wins are all checked before display.

How to use this tool

List your segments, one per line, as a label and a weight.
Set how many spins to work the expectations over.
Read each segment's chance and slice angle.
Note that weights are relative — scaling them all changes nothing.

Understanding the controls

Segments: One per line as a label and a weight. Weights are relative rather than percentages, so 1 and 3 is the same wheel as 10 and 30.
Spins: How many spins to work the expected wins over. It has no effect on the odds themselves — only on the last column.

Common use cases

Working out the real odds on a weighted prize wheel
Setting segment sizes for a spinner that should favour some outcomes
Checking that a wheel's slices actually add up
Explaining why a rare prize needs a very thin slice
Estimating how often each outcome comes up over many spins

How this generator works

A segment's probability is its weight over the total weight, and its slice is that fraction of 360 degrees. Slices are laid out in order, each starting where the last one ended. Before display the probabilities are summed and must come to exactly one, the angles are summed and must come to exactly 360, every slice is confirmed to start where its predecessor finished, and the expected wins are confirmed to total the number of spins.

Randomness and fairness

Nothing here is random. A set of weights gives exactly one set of odds — this computes what a wheel would do rather than spinning one.

For how randomness is produced across the whole site, see how Generate Random works.

Limitations and good to know

This gives the odds of a wheel with these weights; it does not spin it, and the picker tools are the ones for that.
A physical wheel is never exactly fair — friction, balance and where the pointer sits all matter, and none of that is modelled.
Expected wins are averages over many spins; a hundred spins will not divide neatly in these proportions.
Weights must be positive, since a segment with no width is not on the wheel at all.

Privacy and your data

The calculation runs in your browser and your segments are never transmitted, stored or included in analytics.