Roll a dice online: how it works, a little history and games to play

How to use the dice roller

Everything happens on one screen. First choose how many dice you want, from one to six. Then choose the type of die: the classic six-sided cube, or the d4, d8, d10, d12 and d20 used in tabletop role-playing games. Press the big Roll button, or press the Space bar on a keyboard, and the dice tumble across the tray.

When they stop, every die shows its value and the total appears underneath. Each roll is also added to a short list of your last ten rolls, so you can check what happened a moment ago without writing anything down. That list lives only in the open page and disappears when you reload.

• Pick the number of dice, from 1 to 6.
• Pick the die type: d4, d6, d8, d10, d12 or d20.
• Tap Roll or press Space.
• Read each value and the total, then roll again whenever you like.

Why a digital roll is fair

Each result is drawn from your browser's cryptographic random number generator, the same kind of source used for security features, before any animation starts. The tumbling cube is only a way of revealing a number that already exists, so it cannot be nudged by how or when you tap.

There is one subtle trap in turning random numbers into dice, and the roller avoids it. A computer produces random whole numbers in a huge range, about four billion values. If you simply took the remainder after dividing by six, a few faces would get one extra chance, because four billion is not an exact multiple of six. The roller uses a method called rejection sampling: any random value from that small leftover zone is thrown away and drawn again. The result is that every face of every die has exactly the same chance.

A short history of dice

People have been throwing objects to decide things for thousands of years. Some of the earliest gaming pieces were knucklebones, the small ankle bones of sheep and goats, which land on one of four sides. Six-sided dice with dots appear in the ancient cities of the Indus Valley and in Mesopotamia.

The Royal Game of Ur, a board game from ancient Mesopotamia about 4,500 years old, used small four-sided pyramid dice with marked tips. Players counted how many marked points landed face up, which made a roll of two the most likely result. Romans loved dice too. Alongside cubes they threw tali, four-sided knucklebones, and the best throw, where each bone showed a different side, was called the Venus. Gambling with dice was so popular that Roman law tried to restrict it outside festivals.

Polyhedral dice and tabletop role-playing games

The d4, d8, d12 and d20 are based on the Platonic solids, the regular shapes the ancient Greeks studied, while the d10 is a special shape with kite-like faces. They became famous in the 1970s with Dungeons & Dragons, which used a full set of polyhedral dice for attacks, damage and luck. The notation is simple: the number before the d is how many dice to roll and the number after it is how many sides each one has. So 3d6 means three six-sided dice added together, and d20 means one twenty-sided die.

In many role-playing games the d20 decides whether an action succeeds, while smaller dice like the d4 or d8 decide how much damage a dagger or a sword deals. If your set is missing a die, or you are playing online with friends, the roller can stand in for it.

Game ideas to play with dice

You do not need a board to have fun with dice. A few classics work with nothing but the roller and something to write on.

• Five-dice poker style: roll five d6 up to three times, keeping the dice you like, and aim for patterns such as three of a kind, a full house or a straight, in the spirit of Yacht and Yahtzee.
• Pig: roll one die as many times as you dare and add up the points, but a 1 wipes out your turn. First to 100 wins.
• Highest roll goes first: everyone rolls one d20 to decide the turn order of any game.
• Chore roulette: give each chore a number from 1 to 6 and let the die assign the washing up, the bins or the shopping.
• Story dice: roll a d6 for a character, a place and a problem from a list you made together, then tell a short story with the result.

A little probability: why 7 is the lucky number

One fair die gives each face the same chance, one in six for a d6. Add two dice together and things change. There are 36 possible pairs, and six of them make a total of seven (1 and 6, 2 and 5, 3 and 4, and the same pairs reversed), so seven appears about 17 percent of the time. A total of two or twelve needs one exact pair each, so each appears less than 3 percent of the time.

That is why many board games place their most important spaces or resources on six, seven and eight, and why rolling more dice pulls the total towards the middle. With three dice, ten and eleven become the most common totals. Try it yourself: roll two dice twenty times and watch how often the middle totals turn up compared with the extremes. Probability is only a guide for any single roll, though, so keep the dice for games and fun decisions, not for anything important.