How PickSpin picks fairly

1. A secure source of randomness

Every tool on this site gets its randomness from crypto.getRandomValues, a Web Crypto function built into every modern browser. It is a cryptographically secure generator that your operating system seeds from hardware noise, the same source used to make encryption keys. Its output can't be predicted from past results, unlike the everyday Math.random(), whose internal state can in principle be recovered from a handful of outputs.

2. Turning random bits into a fair pick

The generator hands back whole numbers from 0 up to 4,294,967,295 (2³² − 1). To choose one of n options, the obvious move is to take the remainder after dividing by n. That is subtly unfair whenever n doesn't divide the range evenly: the leftover values at the top all land on the first few options, which get a slightly bigger share. It's called modulo bias.

With 2³² values the bias is tiny but real. It's much easier to see with a toy generator that only makes the numbers 0 to 7. Change the number of options and compare:

PickSpin does the same thing with the full 32-bit range: it finds the largest multiple of n below 2³² and redraws on the rare occasions a value lands above it. For a 7-slice wheel that happens about once in a billion draws, so it costs nothing and removes the bias completely. Shuffles (for teams and multi-name draws) use the Fisher–Yates algorithm built on the same unbiased function, so every ordering is equally likely.

We test it, too: the site's test suite draws hundreds of thousands of values and runs a chi-square goodness-of-fit test on every function, including shuffles and no-repeat draws.

3. The wheel lands where the draw says

Many spinner sites run a physics animation and read off whichever slice ends up under the pointer. That ties fairness to the animation code, the frame rate of your device and rounding in slice boundaries. PickSpin reverses the order. Step through it:

The same pattern runs through the whole site: the coin's face, each die, the computer's rock-paper-scissors throw and every drawn name are decided first, and the flicker or tumble you see is played afterwards. Plenty of “obvious” explanations hide a catch, just as the remainder trick does; the Moon’s phases are a classic case, and ahaboo has a narrated explainer on why they really happen.

What fair does not mean

Fair means every option has the same chance on every spin. It doesn't mean results take turns. The same name can come up twice in a row, and over a short run some options won't come up at all. If you need everyone to get exactly one turn, use "Remove each winner" on the wheel or hat mode in the name picker. To see how streaky real randomness is, try the streak simulator on the coin flip page.

PickSpin is for classroom picks, games and everyday choices. It isn't a certified random number generator for lotteries or regulated prize draws.