Tabletop
Dice Roller for D&D
Attack rolls, damage, saving throws and ability checks, with advantage and disadvantage built in. Every roll shows you the real odds behind it, so you know whether that miss was unlucky or just ordinary.
The shape of 1d20
A d20 is flat, which is why fifth edition feels swingy. Turn on advantage above and watch the curve lean towards the high end.
- 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.
Hitting an armor class
Your attack bonus plus a d20 against the target's AC. The table is for a +0 bonus; add your bonus to the AC column to read it off.
| 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% |
Damage dice, with what to expect
Every damage roll links to its full curve.
| Roll | Dice | Average | Range | Max damage |
|---|---|---|---|---|
| Dagger, dart, sling | 1d4 | 2.5 | 1–4 | 25.0% |
| Shortsword, scimitar, handaxe | 1d6 | 3.5 | 1–6 | 16.7% |
| Longsword, rapier, warhammer | 1d8 | 4.5 | 1–8 | 12.5% |
| Longbow, pike, glaive | 1d10 | 5.5 | 1–10 | 10.0% |
| Greataxe | 1d12 | 6.5 | 1–12 | 8.33% |
| Greatsword, maul | 2d6 | 7.0 | 2–12 | 2.78% |
| Sneak attack at level 5 | 3d6 | 10.5 | 3–18 | 0.463% |
| Fireball | 8d6 | 28.0 | 8–48 | 0.000% |
A greatsword's 2d6 averages 7 against 6.5 for a greataxe's 1d12, and it is far more consistent: the axe rolls a 1 8.33% of the time, while the sword's minimum of 2 comes up 2.78% of the time. Buying the sword is buying the middle of the curve.
What a critical hit does to the curve
A critical hit doubles the weapon dice, not the total, so a longsword crit is not a d8 with a bonus, it is 2d8. That changes the shape as well as the size. A single d8 deals 2 or less 25.0% of the time. Two d8s average 9, peak at 9, and land under 5 only 9.38% of the time. The crit is not just bigger, it is more reliable. The famous snake eyes crit is real, at 1 in 64, just rare enough that people remember every one.
The greataxe is where this matters most. A single d12 deals 3 or less 25.0% of the time, which is where the axe's reputation for feeling terrible comes from. Its crit, 2d12, deals 4 or less only 4.17% of the time. The greatsword's crit is 4d6, averaging 14 against the axe's 13, with the same maximum of 24 and a much tighter spread, so the long argument over which two-handed weapon is better comes down to whether you want the reliable crit or the swingy one. Add the barbarian feature that adds another weapon die on a crit and the axe reaches 3d12: average 19.5, 24 or more 26.2% of the time, and a minimum that turns up 1 in 1,728.
Fireball and the big pools
Eight d6 averages 28, a number worth memorising because a referee can resolve most fireballs with it and be close. About 74.0% of casts land between 23 and 33, 0.745% reach 40 or more, and the maximum of 48 is 1 in 1,679,616. Anyone who says they rolled all sixes on a fireball is almost certainly misremembering. On a successful save the damage halves, and because halving compresses the spread too, a saved fireball is a far more predictable outcome than a failed one.
Sneak attack grows the same way, one d6 every two levels, and at 5d6 the maximum of 30 is already 1 in 7,776: plan around 17.5. A hundred foot fall is 10d6, averaging 35, and only 2.52% of falls come in under 25. Big pools are not wild, they are steady: the more dice, the more tightly the total gathers around its average.
Advantage, in numbers
What keeping the higher of two d20 actually does.
- Lowest
- 1
- Highest
- 20
- Average
- 13.82
- Most likely
- 20
- Nat 20 chance
- 9.75%
- Hit 11+
- 75.0%
Advantage is worth roughly +5 in the middle of the range and much less at the extremes. If you need a 2 or better, advantage barely helps because you almost never miss anyway. If you need a 20, it takes you from 5.00% to 9.75%. The biggest lift is around a target of 11, where it turns a coin flip into a three in four. That is why advantage on a mid-difficulty save matters more than a +2.
Common questions
How do you roll with advantage?
To roll with advantage, roll two d20 and keep the higher result. It raises the chance of a natural 20 from 5.00% to 9.75%, and the chance of rolling 11 or better from 50% to 75%. Disadvantage is the same roll keeping the lower die. Toggle either above and the chart follows.
What does 2d6+3 mean?
2d6+3 means roll two six-sided dice, add them together, then add 3. The result runs from 5 to 15 with an average of 10.0. The number before the d is how many dice, the number after is how many sides, and anything after that is a flat modifier.
What are the odds of a natural 20?
The odds of a natural 20 on a single d20 are 5.00%, or 1 in 20. With advantage they rise to 9.75%. Over a session of forty attack rolls, the chance of seeing at least one natural 20 is 87.1%.
Is this roller random enough for real play?
Yes. Every roll uses the Web Crypto API with rejection sampling, which is the same class of randomness used for cryptographic keys, and it avoids the modulo bias that makes some dice apps quietly favour low faces. Nothing is sent to a server and nothing is logged.