Wheel Spinner with Weights
Spin a wheel with weighted segments — exact odds, provable result.
How it works
Spin a decision wheel where each segment can have its own weight (3 × pizza, 1 × sushi). The odds are exactly weight ÷ total, the organiser can publish a SHA-256 fingerprint before the spin, and the result replays identically here.
- Each segment covers weight ÷ total weight of the circle, clockwise from the pointer at 12 o’clock. A uniform number u in [0, 1) picks the point 360° × u that stops under the pointer, so a segment wins with probability exactly weight ÷ total (up to the 32-bit resolution of the generator).
- The wheel turns 4–6 whole turns plus the offset that brings that point under the pointer; the app animates exactly this rotation.
- Fairness proof (commit-reveal): fingerprint = SHA-256 of “fieldday-party-v1|wheel|<segments and settings as sorted JSON>|<secret>”, shown before the spin. The random numbers come from SHA-256 of the secret plus the audience word chosen afterwards; the generator is sfc32.
- With “remove each winner”, later spins use the remaining segments with their weights re-normalised.
For games and everyday decisions. Without a secret the spin is predictable. Not for regulated gambling or lotteries.
Sources
- FIPS 180-4 Secure Hash Standard (SHA-256) (NIST)
- PractRand — the sfc32 small fast counting generator (Chris Doty-Humphrey)
Part of Fieldday
-
Fieldday Sports club & training organiser
Fixtures, brackets, ratings and training plans for your club — in one workspace.
Related tools
- Plinko Name Picker – Drop a ball through pegs to pick a name — fair, replayable and provable.
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- Chore Roulette – Spin a fair chore rota: random but balanced by effort, with a “not again” rule.
How to use the Wheel Spinner with Weights
Spin a decision wheel where every segment can have its own weight, see the exact odds and prove afterwards that the spin was not steered.
What it is for
A wheel is the classic way to settle "what do we eat" or "who goes first". Plain wheels give every option the same share. This wheel lets you give options weights: if three people want pizza and one wants sushi, pizza can take three times as much of the wheel. The tool shows the exact chance of every segment and spins with a commit-reveal proof, so nobody has to trust the person holding the phone.
The same engine draws and animates the wheel in the Party Picks section of Fieldday. There Fieldday creates the secret, shows the fingerprint before the spin and keeps a history of past spins. On this page you can run a spin directly or check a spin made in the app.
Worked example
Dinner for a group: Segments Pizza (weight 3), Sushi (1), Tacos (2), Curry (2), Spins 1, Secret c41d0e9b7a2f, Audience word hungry.
The Segments and chances table shows how the circle is shared: Pizza 37.5 % (0° to 135°), Sushi 12.5 % (135° to 180°), Tacos 25 % (180° to 270°) and Curry 25 % (270° to 360°). The fingerprint published before the spin is 8facf12a…93854313.
The result: "The wheel stops on Curry (chance 25 %)." The pointer lands at 336.735°, inside Curry's range. The wheel turns 1823.265° in total: five whole turns plus the offset that brings that point under the pointer.
The second example uses the wheel for turn order. Four players with weight 1 each, 3 spins and Remove each winner before the next spin switched on give Cleo, Ben, Dev. The chance column grows from 25 % to 33.33 % to 50 % because each spin has one segment fewer.
In a custom run with Board game (weight 2), Karaoke (1) and Film night (3), secret friday-73b1 and word popcorn, the wheel picked Board game, which had a 33.33 % chance.
How to read the result
- Winner or First spin is the segment under the pointer after the first spin. Its chance is that segment's weight divided by the total weight at that spin.
- Segments and chances lists every segment with its weight, its share and its angle range, measured clockwise from the pointer at 12 o'clock.
- Spins shows each spin's winner, its chance at that moment, where the pointer landed and the full wheel rotation.
- Fingerprint input is the exact text whose SHA-256 is the fingerprint. Anyone can hash it and compare it with the value shared before the spin.
Tips and common mistakes
- Empty weights count as 1. Use any positive number up to 1000; decimals such as 0.5 work too.
- Give one segment a bigger weight instead of listing it twice. Duplicate labels are rejected.
- With winners removed you can spin at most one time less than there are segments. Switch removal off to spin the same wheel up to 10 times.
- For a real decision always enter a secret. Without one the tool derives it from the segments and warns that the spin is predictable.
FAQ
Are the odds exactly what the table says?
Yes, up to the 32-bit resolution of the random generator. A uniform number between 0 and 1 picks the point under the pointer, so each segment wins with its share of the circle.
Why add an audience word?
The word is called out after the fingerprint is shown. It changes the spin, so even the organiser cannot know the result in advance or choose a secret that favours one option.
How do I check a spin from Fieldday?
Open the proof under the result in Party Picks, copy the tool input and run it here. The fingerprint, the pointer angle and the winner must be identical.
Can I use it for gambling?
No. It is made for games and everyday decisions and is not suitable for regulated gambling or lotteries.
Guide last updated:
For scripts and AI agents
- JSON API:
POST https://fielddaywheelspinner.usefulweb.app/api/v1/calculate(same calculation as this page) - Interface description: OpenAPI 3.1 · AI guide: llms.txt
- MCP server (Streamable HTTP):
https://fielddaywheelspinner.usefulweb.app/mcp· tool namefieldday_wheel_spinner
Example request
curl -s -X POST https://fielddaywheelspinner.usefulweb.app/api/v1/calculate \
-H 'content-type: application/json' \
-d '{"segments":[{"label":"Pizza","weight":3},{"label":"Sushi","weight":1},{"label":"Tacos","weight":2},{"label":"Curry","weight":2}],"spins":1,"secret":"c41d0e9b7a2f","audienceWord":"hungry"}'