What one click actually rolls
You choose one die type from d4, d6, d8, d10, d12, d20 or d100 and a count from 1 to 100. Every die in the batch is the same type, so there is no notation field: a roll like 2d6+3 is two d6 plus a modifier you add to the total yourself. For each die the tool draws a 32-bit random number, scales it to the range 0 up to 1, and maps it onto the faces with 1 + floor(u * sides). A d10 therefore shows 1 to 10, and a d100 shows 1 to 100 rather than the 00 to 99 of a physical percentile pair. The results panel shows each die, the Total, the dice count and the Average per die. Six-sided dice are drawn as pip faces.
Why several dice do not behave like one
One die is uniform: each face is 1 in N. Add dice together and the total is no longer uniform, because many more combinations reach the middle values than the extremes. With two d6 there are 36 equally likely pairs:
| Total | Ways | Chance |
|---|---|---|
| 2 or 12 | 1 | 2.8% |
| 3 or 11 | 2 | 5.6% |
| 4 or 10 | 3 | 8.3% |
| 5 or 9 | 4 | 11.1% |
| 6 or 8 | 5 | 13.9% |
| 7 | 6 | 16.7% |
The expected total of n dice with s sides is n * (s + 1) / 2, so 2d6 averages 7 and 3d6 averages 10.5. With three dice, a 10 and an 11 each arise 27 ways out of 216 (12.5%), while a 3 or an 18 arises once (about 0.46%). The more dice you roll, the more the totals bunch around the mean, which is why the Average stat hovers near 3.5 for d6 but wanders more on small rolls.
Probabilities worth knowing
- At least one 6 in four d6:
1 - (5/6)^4, about 51.8%. This is the classic even-money bet. - At least one natural 20 when rolling two d20 (advantage in many tabletop games):
1 - 0.95^2, 9.75%, against 5% for a single die. - Rolling the same d20 ten times without a single 20 happens about 60% of the time, so a "cold" stretch is normal.
Common mistakes
- Choosing d10 and expecting 0 to 9. This tool shows 1 to 10; subtract 1 for games that read a d10 as 0 to 9.
- Treating a streak as evidence of bias. Each roll is independent and the previous result has no memory.
- Asking for a number from a range that is not a die size. For that, the random number generator accepts any minimum and maximum, and a coin flip is the quick choice when you only have two outcomes.