Virtual Dice Roller

Dice are among the oldest gaming tools known; six-sided dice with pips have been found at sites in the Indus Valley and Mesopotamia dating back roughly 5,000 years, and earlier peoples cast knucklebones in the same way. On a standard die the opposite faces add up to seven, so 1 is opposite 6, 2 opposite 5 and 3 opposite 4.

A virtual roller gives the same result as a well-made physical die without the risk of dice rolling off the table. Each die here is generated independently, with every face exactly equally likely.

Dice shapes

A fair die has faces that are all equivalent, so each is equally likely to land on top. The five Platonic solids, with 4, 6, 8, 12 and 20 identical faces, make natural fair dice, and together with the ten-sided pentagonal trapezohedron they form the standard set used in games such as Dungeons & Dragons, written d4, d6, d8, d10, d12 and d20. A d4 is read from the point at the top or the edge at the bottom, since no face lands upward. Other fair shapes exist, including two-sided coins, long rolling dice and dice built from other face-transitive solids with 24, 30 or more faces.

How random is a dice?

A physical die is random because its outcome is extremely sensitive to tiny differences in how it is thrown, how it bounces and the surface it lands on, even though the motion obeys deterministic physics. Studies of die rolling suggest that a die needs to bounce and tumble several times before the result becomes effectively unpredictable; a gently rolled die can be biased toward the face that started on top.

Real dice are also not perfectly fair. Drilled pips remove more material from the 6 face than the 1, so on cheap dice with deep pips the 6 is slightly lighter and lands up a little more often, while rounded corners and molding flaws introduce other small biases. Casino dice are machined to tight tolerances with flush, filled pips, transparent material that reveals hidden weights, and sharp edges, and are replaced frequently.

This roller uses crypto.getRandomValues, a cryptographically secure random number generator built into browsers, and maps its output to faces without the slight bias that the naive remainder method introduces. With two dice, the totals are not equally likely: there are six ways to roll a 7 but only one way to roll a 2 or a 12, as the table shows.

Frequently asked questions