How does a buoyancy test determine the fairness of a 6-sided die?

Question

There are a lot of pages and vids out there suggesting that floating dice allows you to tell if they’re fair or not. How does this work?

In: 1

Answer 1

A weighted die is more likely to roll a certain number than others. This refers to literal weight, where one side is heavier and so more likely to land down while the opposite side is lighter and more likely to land up.

Floating dice will let you check to see if one side of the die is heavier as it will preferentially float with that side down. For example if you are suspicious that a 6-sided die is weighted on the 1 side so that it rolls 6 more often, if it will float on the 4 side then you know the 1 side isn’t heavier than the 6.