Is an Online Spinning Wheel Really Random? How Spin Master Picks a Winner

How a spin works

1. When you click spin, your browser asks its built-in secure random number generator (the Web Crypto API) for a number.
2. That number decides how many degrees the wheel will turn beyond five full rotations.
3. The wheel animates for about five seconds and comes to rest at that angle.
4. The winner is the slice under the pointer.

What this means

The outcome is decided at the instant you click. The five-second animation is the show: it lands exactly where the random angle says it should. Because the angle comes from the secure generator rather than from the speed or timing of your click, nobody can influence or predict the result by clicking at a particular moment.

Spin Master does not use Math.random, the simpler generator that browsers also provide, to choose a result. The secure generator is designed for security uses and is far less predictable.

Are all slices equally likely?

All slices are the same size, so each name has the same chance. We tested this with a simulation: 1,000,000 spins for each of several wheel sizes, using the same winner calculation the site uses. Every slice's share landed within about 0.15 percentage points of its ideal share. With 7 equal slices the ideal share is 14.29% and the measured shares ranged from 14.26% to 14.32%. With 11 slices (ideal 9.09%) they ranged from 8.99% to 9.14%.

If you want some names to be more likely, add them more than once. A name entered three times has three slices and three times the chance, which is useful for bonus entries and is visible to anyone watching.

What about Meeting Rooms?

In a Meeting Room, the device that spins sends the final angle and the list to the others. Every device then works out the winner from those same two facts using the same calculation, so everybody sees the same result at the same moment. Guests cannot change the outcome, and the host's list is the list everyone sees.

What this does not prove

An online wheel is not an audited lottery. Nobody can verify from the outside that you did not edit the list or spin more than once. For regulated draws, follow the rules that apply to you and use an approved method.

Keeping your own draws honest

• Show the full list before you spin
• Spin once per decision and accept the result
• Record your screen when stakes are high
• Write down in advance how many winners there will be and how ties or no-shows are handled