Are all dice fair?

Not all dice are equally fair: almost none are perfectly balanced, although with most dice you won’t notice the difference during a game. Precision dice, with sharp edges and pips filled with paint of the same weight, are the best balanced; cheap dice with recessed pips may have a very slight bias.

The problem with pips

On many dice, the pips are holes. The six face has six holes and the one face has just one, so the six face weighs a little less. This can make the six land face up slightly more often. The difference is tiny and only becomes apparent over thousands of rolls.

Rounded edges

Rounded corners make a die roll further, but if the rounding is uneven, it can favour certain faces. Precision dice have sharp edges and are made to very strict tolerances.

How to test a die

Here’s a test you can try at home: put it in a glass of very salty water and spin it several times. If the same face always ends up on top, something is wrong. A more rigorous test is to roll it hundreds of times and record the results.

Accidental bias or deliberate tampering?

An imperfect die is one thing; a deliberately rigged die is another. We discuss that in loaded dice: history and cheating. If you’d like a refresher on how dice should behave, read how dice probabilities work.