D20 roller
Roll a d20 with your modifier, or roll with advantage or disadvantage. Natural 20s and 1s are called out.
Choose a mode and roll.
Roll log
Rolls appear here, newest first.
Advantage in numbers
Advantage is worth more than it looks. Rolling two d20s and keeping the higher changes the odds of hitting a target number like this (the chance of rolling at least that number on the die):
| Need at least | Normal | Advantage | Disadvantage |
|---|---|---|---|
| 2 | 95% | 99.8% | 90.3% |
| 5 | 80% | 96.0% | 64.0% |
| 8 | 65% | 87.8% | 42.3% |
| 10 | 55% | 79.8% | 30.3% |
| 11 | 50% | 75.0% | 25.0% |
| 13 | 40% | 64.0% | 16.0% |
| 15 | 30% | 51.0% | 9.0% |
| 18 | 15% | 27.8% | 2.3% |
| 20 | 5% | 9.8% | 0.3% |
The boost is biggest in the middle: needing an 11, advantage takes you from 50% to 75%. At the extremes it matters less. A rough rule used by many players: advantage is worth about +5 when you need around a 10, less when you need a very high or very low roll.
Need other dice for your character sheet? The dice roller does d4 to d100 with totals, such as 8d6 for a fireball.
Questions people ask
How does advantage work in D&D?
In D&D 5th edition, advantage means you roll two d20s and keep the higher; disadvantage means you keep the lower. Then you add your modifier. Choose the mode and this roller shows both dice and which one counts.
How much does advantage help?
On average it adds about 3.3 to a straight d20 roll (13.8 instead of 10.5), and the chance of a natural 20 rises from 5% to 9.75%. Disadvantage drops the average to about 7.2 and the chance of a natural 1 rises to 9.75%.
Is a digital d20 fairer than a real one?
Cheap plastic d20s are often slightly unbalanced from air bubbles or uneven faces. This roller gives each number exactly a 1 in 20 chance using crypto.getRandomValues with rejection sampling.
What counts as a critical hit?
A natural 20 (the die shows 20 before modifiers) on an attack roll is a critical hit in 5e; a natural 1 always misses. The roller flags both.