Dice notation
Tabletop games describe dice rolls in a shorthand that looks cryptic until you know it. The format is a number, the letter d, and the number of sides — so 2d6 means roll two six-sided dice and add them together. A modifier is appended, so 1d20+5 means roll one twenty-sided die and add five.
This notation comes from Dungeons & Dragons and is now standard across most tabletop games, board games and role-playing systems.
The standard polyhedral set
A typical RPG set contains seven dice: d4, d6, d8, d10, d12, d20 and a percentile d10. Each has a role. The d20 resolves most actions in D&D, the d6 is the familiar cube used in most board games, and the d100 (rolled as two d10s or as a single hundred-sided die) generates percentage outcomes on random tables.
Why 2d6 is not the same as 1d12
Both produce a range topping out at twelve, but the distributions are completely different, and this is the most useful thing to understand about dice.
A single d12 is flat — every result from one to twelve is equally likely. Two d6 produce a bell curve: seven comes up six times out of thirty-six, while two and twelve each appear only once. Rolling seven is six times more likely than rolling twelve.
Game designers use this deliberately. Flat distributions produce swingy, unpredictable outcomes. Bell curves cluster results around the average, making the game feel more consistent and rewarding character bonuses more reliably. When a system uses 3d6 rather than 1d20, that is a design decision about how random the game should feel.
Advantage and disadvantage
These mechanics roll twice and keep the better or worse result. Advantage on a d20 raises the average roll from 10.5 to about 13.8 — worth roughly a plus-four bonus, though it helps most in the middle of the probability range and barely at the extremes.
Is a virtual roller fair?
It is arguably fairer than physical dice. Real dice are subject to manufacturing tolerance, wear, and the hollow pips on cheap d6s making the six face marginally lighter. This roller uses cryptographic randomness with rejection sampling to eliminate modulo bias, so every face is exactly equally likely.
What it cannot replace is the social element of a physical roll in front of other players, which is a real part of why people prefer dice at the table.
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Frequently Asked Questions
What does 2d6+3 mean?
Roll two six-sided dice, add them together, then add three to the total.
Why does 2d6 feel different from 1d12?
A single die gives a flat distribution where every result is equally likely. Two dice produce a bell curve clustered around seven, making extreme results rare.
How much is advantage worth?
On a d20 it raises the average from 10.5 to about 13.8, roughly equivalent to a plus-four bonus, though the benefit is largest in the middle of the range.
Are virtual dice as fair as real ones?
Arguably fairer. Physical dice have manufacturing imperfections and wear. This uses cryptographic randomness with bias correction.
Can I roll many dice at once?
Yes, up to 100 at a time, with the individual results shown alongside the total.