Roll a d20
A twenty-sided dice roller for D&D and tabletop games, with advantage, disadvantage and modifiers.
Tap roll
How to use the roll a d20
- Tap Roll or press the space bar to roll one d20.
- Choose Advantage or Disadvantage to roll two d20s and keep the higher or lower.
- Add your ability or attack modifier, for example +5, and flipj adds it to the result.
Natural 20s and natural 1s
In Dungeons & Dragons 5th edition, rolling a 20 on the die itself (a "natural 20") on an attack roll is a critical hit, and a natural 1 always misses. flipj highlights both so you never miss one. Each number has a 1 in 20 (5%) chance on any roll.
Advantage and disadvantage
With advantage you roll two d20s and use the higher; with disadvantage you use the lower. Advantage raises your chance of a natural 20 from 5% to 9.75%, and raises the average roll from 10.5 to about 13.8. Disadvantage lowers the average to about 7.2.
Is a virtual d20 fair?
flipj uses your browser's built-in cryptographic random number generator (crypto.getRandomValues), the same source browsers use for encryption keys. We also avoid "modulo bias", a subtle flaw where some results come up slightly more often than others. Every result is generated on your device, so nothing you enter is sent to us.
Questions
What is the average roll on a d20?
10.5. Each number from 1 to 20 is equally likely, so the average is (1 + 20) ÷ 2.
What are the odds of rolling a natural 20?
1 in 20, or 5%, on a single roll. With advantage it rises to 9.75%.