From D4 to D20: Rolling Dice Online
A standard tabletop set has seven dice: d4, d6, d8, d10, d12, d20 and a percentile d10. The Dice Roller covers them all, singly or in bulk.
Why so many shapes
Each die is a Platonic solid or close to one, chosen because every face has an equal chance. The d4 is a tetrahedron, the d6 a cube, the d8 an octahedron, the d12 a dodecahedron and the d20 an icosahedron. The d10 is not a Platonic solid - it is two pentagonal pyramids stuck together, which still gives ten equal faces.
The d20 dominates modern roleplaying because twenty faces give a 5 per cent step per number, which is a convenient granularity for deciding whether something succeeds. Smaller dice are used for damage and for effects where the spread matters more than the precision.
One die is flat, several are not
This is the most useful thing to understand about dice, and it is routinely missed.
One d20 is uniform: every number from 1 to 20 is equally likely. There is no "average" roll in any meaningful sense, and a 1 is exactly as likely as an 11.
Three d6 is not uniform at all. The total runs from 3 to 18, and 10 and 11 are far more likely than either extreme - there is exactly one way to roll a 3 and twenty-seven ways to roll a 10. So 3d6 clusters hard in the middle, while 1d18 spread over the same range would be flat.
That difference is why game designers pick between them deliberately. One large die means wild swings; several small dice mean predictable results with rare extremes. It is the same principle that makes an average of several measurements more reliable than one - which the Average / Median Calculator is built on.
Streaks are normal and feel rigged
In twenty rolls of a d6, some faces will come up four times and some not at all. That is what randomness looks like, and a sequence with exactly three or four of each would be the suspicious one.
Which is why every roleplaying group contains someone convinced their dice are cursed. Over a long enough session, a run of bad rolls is close to guaranteed, and human memory keeps the bad run and discards the ordinary stretch either side.
Physical dice are not perfectly fair
Worth knowing. Cheap injection-moulded dice have rounded edges, uneven pips drilled out of one side, and small voids from the moulding - all of which bias them slightly. Casino dice are machined to tight tolerances with flush-filled pips for exactly this reason.
A digital roll has none of those problems, and loses the satisfying part. Which is the honest trade.
Common questions
What does 2d6+3 mean?
Roll two six-sided dice, add them, add three. Standard notation across tabletop games.
What is a percentile roll?
Two d10s read as tens and units, giving 1 to 100. One die is usually marked 00 to 90.
Is the online roll genuinely random?
It uses the browser's random number generator, which is more than adequate for a game.
Why does my d20 seem to roll low?
It does not. Twenty faces means long runs of bad luck are common and memorable.
Need a roll?