Free tool
Dice Roller
Roll up to twelve dice at once, from d4 to d100. Each die is shown separately and totalled, with no physical set required.
Die
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Pick a die, then roll
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What the different dice are for
The six-sided die is the one most households own, and for most purposes it is the only one needed: a d6 settles who goes first, how many spaces to move, or which of six options to take. The rest of the set exists because tabletop role-playing games need a range of probability shapes rather than a single one.
The twenty-sided die is the workhorse of that tradition. A d20 produces a flat distribution across twenty outcomes, which suits a single pass-or-fail check against a target number: the chance of rolling 15 or higher is exactly six in twenty, and everyone at the table can work that out without arithmetic. The d100, rolled here as a single hundred-sided draw, does the same job at percentage resolution.
Smaller dice tend to be used for damage and duration rather than checks. A d4 is the shape people remember for stepping on, a d8 and d12 sit between the extremes, and the d10 is unusual in being the only die in the set that maps neatly onto our counting system, which is why percentile rolls were traditionally made with two of them.
Rolling several dice changes the shape of the result
This is the part that surprises people. One d6 gives every number from 1 to 6 an equal chance. Two d6 do not: totals cluster hard in the middle, because there are six different ways to make 7 and only one way to make 2. Seven comes up about one roll in six, while snake eyes comes up one in thirty-six.
The more dice you add, the tighter that clustering becomes. Three d6 produce totals between 3 and 18, but almost half of all rolls land between 9 and 12. Board games exploit this deliberately. A game that asks for two dice is a game about a predictable middle with rare extremes; a game that asks for one is a game about genuine swings.
You can watch it happen above. Set the count to six, roll a dozen times, and notice how rarely the total strays far from 21. Then set it back to one and watch the results scatter.
Using dice to make a decision
A die is the right tool when you have more than two options and no clear favourite. Number the options, pick the die that matches, roll once and commit. The awkward case is a number of options that does not match a standard die: with five choices, roll a d6 and re-roll a six. Do not be tempted to map two faces to one option, which quietly doubles that option’s chances.
The same caveat applies here as everywhere else on this site. Randomness is for decisions where the cost of deliberating exceeds the cost of choosing wrongly. If a decision is expensive, slow or hard to reverse, put the dice away and read the frameworks guide instead.