Decision Wheel

about this tool

Options in, one of them out

Type what you are choosing between, one per line, and spin. Every slice is the same size, so every option is equally likely. To give something two chances, put it on the wheel twice.

Up to 60 options fit. Past 24 the labels stop fitting on the slices, so they are left off and the winner is named underneath instead of being squeezed onto a sliver.

The order things happen in

The winner is drawn first, from the browser's cryptographic random source, and the wheel is then turned so that it stops on that slice.

The obvious way round is to spin by a random amount and read off whatever ends up under the pointer. It sounds more like a real wheel and it is worse, because the odds then depend on the easing curve, the frame rate and the rounding of the final angle rather than on the draw. Doing the draw first makes the fairness a property of the randomness rather than of the animation.

The angle arithmetic is the part that has to be right, so the test suite checks the round trip: for every wheel size, every slice, and several starting angles, the slice under the pointer after the turn is the slice that was drawn.

Why it looks like a fairground

The rest of the site is plain on purpose, but a wheel is a toy, so this one is painted like a fairground prize wheel: red, cream, teal and navy slices in a rim of bulbs. The winning slice turns gold when it stops, and its name is written underneath as well, so the colour is never the only way to tell which one won.

Why the ticking is arithmetic

The wheel ticks as it turns, unless you switch Sound off, and the ticks are worked out rather than played at a fixed interval.

A real wheel ticks once per peg and slows as it goes, so the gaps stretch towards the end. A tick here is a peg passing the pointer, so tick i falls when the wheel has covered i/n of its angle. The wheel eases out on 1-(1-t)³, so the time at which it reaches a given fraction is that curve's inverse, and the ticks spread apart as it slows instead of bunching at the end.

Evenly spaced ticks under a decelerating wheel sound like a metronome taped to it, which is the giveaway that the sound and the motion were built by different people. The noise itself is synthesised, so nothing is downloaded for it.

What it cannot do

There are no weights, no saved wheels and no record of past spins. Nothing is stored on your device, so a refresh puts the sample list back and yours is gone; keep your list somewhere else if you need it again.

It also cannot prove anything to anyone. If someone stands to lose by the result, no amount of spinning shows them the answer was not chosen first, which it was.

The random picker makes the same draw without the wheel, which is faster once the list is longer than a wheel can label.

questions

Does the wheel tick as it spins?

Yes, unless you switch Sound off. The ticks are worked out from the inverse of the wheel’s own ease-out rather than played at a fixed interval, so they stretch apart as it slows the way a real wheel does — evenly spaced ticks under a decelerating wheel sound like a metronome taped to it. The noise is synthesised, so nothing is downloaded.

Is the wheel actually random?

Yes, and in the order that matters: the winner is drawn first from the browser’s cryptographic random source, then the wheel is turned so it stops there. Spinning by a random amount and reading off the result would make the odds depend on the easing curve rather than the draw.

Does a bigger slice have a better chance?

Every slice is the same size, so every option is equally likely. There are no weights. To give something two chances, put it on the wheel twice.

How many options can it take?

Up to 60. Past 24 the labels stop fitting on the slices, so they are left off and the winner is named underneath instead.

Can I save my wheel?

No. Nothing is stored on your device and nothing is sent anywhere, so a refresh puts the sample list back and yours is gone. Keep your list somewhere else and paste it back.

Can I use it to settle a dispute?

For a friendly one, yes. For anything someone could contest, no: a web page cannot prove to the loser that it did not choose before it started turning.