How to use it
Type the lowest and the highest total you want in the two boxes above the dice. The roller works out the dice, sets them in the picker with the modifier, and shows the odds of every total in the Probability panel. Press Roll, tap the table or press R to throw them. The same two boxes, under “Number range”, are in the custom roll on every other roller on this site.
How the dice are chosen
A die adds at least 1 and at most its number of sides to a total, so each die widens the range by its sides minus one: a d6 by 5, a d20 by 19, a d100 by 99. To cover a range, the roller finds dice whose widths add up to the gap between your two numbers, then adds or subtracts a modifier so that the lowest possible total lands on your lower limit.
Take 1 to 50. The gap is 49, and 19 + 19 + 11 = 49, so two d20s and a d12 fit. On their own they roll 3 to 52; taking away 2 makes it exactly
1 to 50, which is 1d12+2d20-2. The roller always uses the fewest dice that fit, then the fewest different sizes, so
2 to 12 is the familiar 2d6 rather than a d4 and a d8.
| Range | Dice | Chance of the lowest total |
|---|---|---|
| 1–6 | 1d6 | 1 in 6 |
| 5–10 | 1d6+4 | 1 in 6 |
| 2–12 | 2d6 | 1 in 36 |
| 3–18 | 3d6 | 1 in 216 |
| 0–9 | 1d10-1 | 1 in 10 |
| 1–20 | 1d20 | 1 in 20 |
| 1–30 | 2d10+1d12-2 | 1 in 1,200 |
| 1–50 | 1d12+2d20-2 | 1 in 4,800 |
| 1–100 | 1d100 | 1 in 100 |
Why middle totals come up more often
A single die is flat: every face has the same chance. As soon as two or more dice are added together, a total in the middle can be made in more ways than one at either end. On 3d6 a 3 needs three 1s, one way out of 216, while a 10 can be made 27 ways, so a 10 or an 11 is 27 times as likely as a 3 or an 18. The chart in the Probability panel shows the exact curve for your range.
That shape is often what a game wants: ordinary results common, extreme ones rare. When a range needs only one die (4, 6, 8, 10, 12, 20 or 100 numbers, such as 1 to 20 or 5 to 10) every number is equally likely.
Ranges real dice cannot make
Each die widens a range by an odd number of at least 3, so no mix of dice covers exactly 2, 3 or 5 numbers. For those the roller uses a flat d2, d3 or d5, drawn on screen rather than thrown in 3D. At the table you can get them from ordinary dice:
- 2 numbers, like a coin: roll any die, and read odd as 1 and even as 2.
- 3 numbers: roll a d6 and halve it, rounding up, so 1–2 is 1, 3–4 is 2 and 5–6 is 3.
- 5 numbers: roll a d10 and halve it, rounding up.
When every number must be equally likely
For a fair pick, like a raffle ticket or a random page, a sum of dice is the wrong tool, because the middle numbers win too often. Type
1d50 in the notation box instead: the roller draws a flat 50-sided die on which every number has a 2% chance. With real dice,
roll a d100 and halve it, rounding up, and each number from 1 to 50 comes from exactly two results. When the count of numbers does not go into 100
evenly, re-roll the leftovers: for 1 to 30, roll a d100 and re-roll 91 to 100, then take 30 or 60 off anything above 30.