Roll 1d100
A d100 is almost never a hundred-sided solid. You roll two ten-sided dice, one read as tens and one as units, and put them together into a number from 00 to 99 with 00 counting as 100. Solid hundred-sided balls exist, but they roll for an uncomfortably long time.
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Rolling 1d100 gives a result from 1 to 100, and on a fair die each one is equally likely at 1%. There is no curve and no typical result to plan around. The average sits at 50.5, which is a number the die itself can never show.
- Minimum
- 1
- Maximum
- 100
- Mean
- 50.5
- Median
- 50.5
- Std deviation
- 28.87
- Chance per result
- 1%
1d100 probability distribution
One die means one way to make each result, so the chart is a flat line rather than a curve. Add a second die and the totals immediately start clustering.
| Total | Ways | Probability | This or lower |
|---|---|---|---|
| 1 | 1 | 1% | 1% |
| 2 | 1 | 1% | 2% |
| 3 | 1 | 1% | 3% |
| 4 | 1 | 1% | 4% |
| 5 | 1 | 1% | 5% |
| 6 | 1 | 1% | 6% |
| 7 | 1 | 1% | 7% |
| 8 | 1 | 1% | 8% |
| 9 | 1 | 1% | 9% |
| 10 | 1 | 1% | 10% |
| 11 | 1 | 1% | 11% |
| 12 | 1 | 1% | 12% |
| 13 | 1 | 1% | 13% |
| 14 | 1 | 1% | 14% |
| 15 | 1 | 1% | 15% |
| 16 | 1 | 1% | 16% |
| 17 | 1 | 1% | 17% |
| 18 | 1 | 1% | 18% |
| 19 | 1 | 1% | 19% |
| 20 | 1 | 1% | 20% |
| 21 | 1 | 1% | 21% |
| 22 | 1 | 1% | 22% |
| 23 | 1 | 1% | 23% |
| 24 | 1 | 1% | 24% |
| 25 | 1 | 1% | 25% |
| 26 | 1 | 1% | 26% |
| 27 | 1 | 1% | 27% |
| 28 | 1 | 1% | 28% |
| 29 | 1 | 1% | 29% |
| 30 | 1 | 1% | 30% |
| 31 | 1 | 1% | 31% |
| 32 | 1 | 1% | 32% |
| 33 | 1 | 1% | 33% |
| 34 | 1 | 1% | 34% |
| 35 | 1 | 1% | 35% |
| 36 | 1 | 1% | 36% |
| 37 | 1 | 1% | 37% |
| 38 | 1 | 1% | 38% |
| 39 | 1 | 1% | 39% |
| 40 | 1 | 1% | 40% |
| 41 | 1 | 1% | 41% |
| 42 | 1 | 1% | 42% |
| 43 | 1 | 1% | 43% |
| 44 | 1 | 1% | 44% |
| 45 | 1 | 1% | 45% |
| 46 | 1 | 1% | 46% |
| 47 | 1 | 1% | 47% |
| 48 | 1 | 1% | 48% |
| 49 | 1 | 1% | 49% |
| 50 | 1 | 1% | 50% |
| 51 | 1 | 1% | 51% |
| 52 | 1 | 1% | 52% |
| 53 | 1 | 1% | 53% |
| 54 | 1 | 1% | 54% |
| 55 | 1 | 1% | 55% |
| 56 | 1 | 1% | 56% |
| 57 | 1 | 1% | 57% |
| 58 | 1 | 1% | 58% |
| 59 | 1 | 1% | 59% |
| 60 | 1 | 1% | 60% |
| 61 | 1 | 1% | 61% |
| 62 | 1 | 1% | 62% |
| 63 | 1 | 1% | 63% |
| 64 | 1 | 1% | 64% |
| 65 | 1 | 1% | 65% |
| 66 | 1 | 1% | 66% |
| 67 | 1 | 1% | 67% |
| 68 | 1 | 1% | 68% |
| 69 | 1 | 1% | 69% |
| 70 | 1 | 1% | 70% |
| 71 | 1 | 1% | 71% |
| 72 | 1 | 1% | 72% |
| 73 | 1 | 1% | 73% |
| 74 | 1 | 1% | 74% |
| 75 | 1 | 1% | 75% |
| 76 | 1 | 1% | 76% |
| 77 | 1 | 1% | 77% |
| 78 | 1 | 1% | 78% |
| 79 | 1 | 1% | 79% |
| 80 | 1 | 1% | 80% |
| 81 | 1 | 1% | 81% |
| 82 | 1 | 1% | 82% |
| 83 | 1 | 1% | 83% |
| 84 | 1 | 1% | 84% |
| 85 | 1 | 1% | 85% |
| 86 | 1 | 1% | 86% |
| 87 | 1 | 1% | 87% |
| 88 | 1 | 1% | 88% |
| 89 | 1 | 1% | 89% |
| 90 | 1 | 1% | 90% |
| 91 | 1 | 1% | 91% |
| 92 | 1 | 1% | 92% |
| 93 | 1 | 1% | 93% |
| 94 | 1 | 1% | 94% |
| 95 | 1 | 1% | 95% |
| 96 | 1 | 1% | 96% |
| 97 | 1 | 1% | 97% |
| 98 | 1 | 1% | 98% |
| 99 | 1 | 1% | 99% |
| 100 | 1 | 1% | 100% |
When you'd roll 1d100
Percentile rolls suit anything that needs fine control. Call of Cthulhu gives you a skill as a percentage and asks you to roll at or under it, so a rating reads as your odds directly with no arithmetic. Random tables use the same range to make some entries common and others genuinely rare, which is hard to do with a small die. Loot generators lean on it for the same reason.
Where this roll shows up
- Call of Cthulhu, where every skill is a percentage you roll under
- Warhammer Fantasy Roleplay and RuneQuest, both percentile systems
- Loot tables, random encounter tables and anything else that needs fine-grained odds
1d100 questions
How do you roll a d100 with two dice?
Pick one d10 as the tens die and one as the units die, ideally a set where the tens die is printed 00, 10, 20 and so on. Roll both, read the tens first, and combine. Two zeros together are read as 100, not zero.
Is there a real hundred-sided die?
Yes. The Zocchihedron is a hundred-faced ball named after its designer, Lou Zocchi. It exists and it works, but it rolls for a long time and the results have been argued over for decades, so most tables stick with two d10s.
Why do percentile systems roll under instead of over?
Because the skill number becomes the answer. If your rating is written as a percentage, rolling at or under it means the number on your sheet is your chance of success, with nothing to add up. That readability is the whole appeal of a percentile system.
What is a d100 used for outside role-playing games?
Anywhere you want fine-grained randomness: raffle draws, random selection from a long list, teaching probability, or settling something with more granularity than a coin. Any single result is genuinely rare, which is the point.