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 is grey

The site has one accent colour, so the wheel is drawn in the warm greys of the rest of the page and only the winning slice turns green when it stops. A wheel of twelve colours would look like a different website.

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 gives you an empty wheel; 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

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 gives you an empty wheel. 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.