Dice Roller

This dice roller throws virtual dice for you — anything from a single d4 to a fistful of d20s — with an optional modifier added to the total and a running history of your last rolls. It covers the full set of polyhedral dice used at the table (d4, d6, d8, d10, d12, d20, and the d100 percentile), lets you roll up to 20 dice at once, and highlights every natural maximum and natural 1 so critical results jump out. It is made for Dungeons & Dragons and other tabletop RPG players who have lost or forgotten their physical dice, for board-game nights, for teachers and students running probability experiments, and for anyone who needs a quick, fair random number without hunting for an app.

Standard dice notation (NdM)

Tabletop games describe dice with the shorthand NdM, where N is how many dice you roll and M is the number of sides on each. So 2d6 means "roll two six-sided dice and add them up," and 4d8 means "roll four eight-sided dice and total them." A modifier is written after the dice: 1d20+5 means roll one twenty-sided die and add 5 to the result, while 2d6−1 subtracts 1 from the sum of two d6. A single die is sometimes written d20 rather than 1d20 — they mean the same thing.

How the dice behave and the probabilities

Each die is independent and fair: on a single dM every face from 1 to M is equally likely, so the chance of any particular number is 1/M. On a d20 that is 1 in 20, or 5% — the basis of the famous "natural 20." The smallest total you can roll on NdM is N (every die shows 1) and the largest is N × M (every die shows its top face); the calculator displays both of these bounds for the dice you have selected. Adding more dice does not just raise the total — it changes the shape of the odds. One d6 is flat (each result equally likely), but the sum of 2d6 forms a triangle peaking at 7, because there are more ways to make 7 (six combinations) than to make 2 or 12 (one each). The average of a single fair dM is (M + 1) ÷ 2, so a d6 averages 3.5 and a d20 averages 10.5; for NdM the expected total is N × (M + 1) ÷ 2.

Worked example

Say your character makes an attack roll of 1d20+5 and the screen shows a 14 on the die. The displayed total is 14 + 5 = 19. To beat an enemy with armour class 17 you need the final total to reach 17 or more, so 19 hits. If instead you roll damage as 2d6+3 and the two dice come up 4 and 5, the total is 4 + 5 + 3 = 12 damage. Over many such rolls the 2d6 part will average 7 (its expected value), so 2d6+3 averages about 10 damage per hit.

Uses beyond RPGs and tips

• Board games: replace lost dice for Ludo, Snakes & Ladders, Monopoly, Catan, and Yahtzee-style games.
• Classroom probability: roll many times to see theoretical odds (like the 2d6 bell curve) emerge in practice.
• Fair decisions: pick a chore, settle a tie, or choose a restaurant by assigning options to numbers.
• Random tables: use a d100 for percentage-based loot, encounter, or event tables.

Use the modifier field for stat bonuses or penalties rather than doing the maths in your head, and read the per-die results, not just the sum, when a rule cares about individual dice (such as rerolling 1s or scoring each die separately). The roll history is handy when you want to compare several attempts or prove a result to other players, and rolling a large number of dice at once is the quickest way to watch probability theory turn into a real bell-shaped curve in front of you.