Spin the Wheel

Three mistakes people make with a spin wheel

1. Thinking you're picking a slice, when you're picking an angle. The wheel doesn't select an option — it lands on a radian. If you add a 13th option to a wheel built for 12 evenly-sized sectors, the underlying code has to either re-divide 360° by 13 (14 of them are a non-terminating 27.692°, so the visual labels may not align with the rendered slices) or give the new slice a weird width. Always count your sectors after editing. This tool re-partitions on every add/remove, but spot-check it.

2. The spin length feels fair, but it isn't random. To look good, most wheels pick a target angle first, then animate 5–10 full rotations ending on it — the rotations are cosmetic. That's how this tool works too (~1800–3600° of rotation before easing to a Math.random()-picked angle). A long spin doesn't make the result more random; it gives your brain time to lock in a preferred outcome, which is why losing a 6-second spin feels worse than losing a coin flip. That's the anchoring bias, not a bug.

3. "Remove the winner" creates a bias you didn't expect. After a winning spin, if you delete that sector, the remaining sectors get larger — each survivor's probability jumps from 1/n to 1/(n−1). For contests where you draw multiple winners in sequence, this is correct (sampling without replacement). For "best of three" decisions, it's wrong; you want replacement, so leave the slices alone. Edge case: with only 2 options left, both have exactly 50% — the wheel is now a coin flip, just slower.