Single die
Roll a d20
A 20-sided die, rolled in your browser. Every face has an equal 5.00% chance, which works out to 1 in 20.
The odds on a d20
A single die is flat: no total is more likely than any other. The curve only appears once you roll more than one, which is what the 2d20 page is for.
- Lowest
- 1
- Highest
- 20
- Average
- 10.50
- Each face
- 5.00%
- Odds
- 1 in 20
Every bar the same height. That flatness is the whole point of a single die: 5.00% per face, no favourites.
What a d20 is for
The one that matters. Attack rolls, saving throws, ability checks, and every moment the table goes quiet.
Hitting a target number
What a flat d20 beats, and how much two-dice advantage moves it.
| Need | Flat | Advantage | Disadvantage |
|---|---|---|---|
| 2+ | 95.0% | 99.8% | 90.2% |
| 4+ | 85.0% | 97.8% | 72.2% |
| 6+ | 75.0% | 93.8% | 56.2% |
| 8+ | 65.0% | 87.8% | 42.2% |
| 10+ | 55.0% | 79.8% | 30.2% |
| 12+ | 45.0% | 69.8% | 20.2% |
| 14+ | 35.0% | 57.8% | 12.2% |
| 16+ | 25.0% | 43.8% | 6.25% |
| 18+ | 15.0% | 27.8% | 2.25% |
| 20+ | 5.00% | 9.75% | 0.250% |
How to use this roller
Tap the die or press the roll button. To roll several at once, change How many. To add a bonus, put it in Modifier: entering 3 turns a d20 into 1d20+3. Negative numbers work for penalties. The keyboard shortcut is R.
Nothing is stored on a server and no account is needed. The page works offline once loaded, which matters if the venue has poor signal.
Common questions about the d20
What are the odds of rolling a 20 on a d20?
Exactly 5.00%, or 1 in 20. Every face on a fair d20 is equally likely, so a 20 is no rarer than a 7.
What is the average roll on a d20?
10.5. That is the midpoint of 1 and 20, and it is worth knowing because the average of a die is always (sides + 1) divided by 2. Over many rolls your results converge on it, but any single roll tells you nothing.
Does rolling with advantage change the odds of a 20?
Yes. Rolling two d20 and keeping the higher lifts your chance of a 20 from 5.00% to 9.75%, close to double. It helps most in the middle of the range: your odds of hitting the halfway mark or better go from 50% to 75%.
Is this d20 roller actually random?
Every roll comes from the Web Crypto API rather than Math.random, and uses rejection sampling to discard values that would skew the result. A plain modulo of a random number is biased when the range does not divide evenly, which for a d20 would quietly favour the low faces.