D&D Dice Roller
Roll D&D dice in standard notation (1d20+5, 4d6kh3, 8d6) with advantage or disadvantage, and see the exact odds of meeting an AC or DC.
This roller reads the dice notation used at Dungeons & Dragons tables: 1d20+5 for an attack, 8d6 for a fireball, 4d6kh3 for ability scores, and advantage or disadvantage with one switch. Each press of Calculate rolls fresh dice with your browser's cryptographic random generator, and next to the result you get the exact average, the range and the chance of meeting or beating a target AC or DC.
How to use this tool
- Type the dice, for example
1d20+5,2d6+3or1d8+1d6+2. - Switch the d20 roll to advantage or disadvantage if your character has it.
- Enter the AC or DC you need to see your exact chance.
- Press Calculate to roll again. Set "How many times" to 6 with
4d6kh3to roll a set of ability scores.
Formula
Average of NdS = N × (S + 1) ÷ 2
With advantage, P(d20 ≥ T) = 1 − ((T − 1) ÷ 20)²; with disadvantage it is ((21 − T) ÷ 20)². For manageable expressions it combines probability tables; large cases show the mean and range without exact odds. kh and kl keep the highest or lowest dice; dl and dh drop them.
Example
An attack of 1d20+5 against AC 15 needs 10 or more on the die: 11 of the 20 faces, a 55% chance. With advantage you roll two d20s and keep the higher, so the chance becomes 1 − (9 ÷ 20)² = 79.75%. Rolling ability scores with 4d6kh3 averages 12.24 per score.
Frequently asked questions
What does 4d6kh3 mean?
Roll four six-sided dice and keep the highest three, the classic way to roll ability scores. 4d6dl1 (drop the lowest one) gives the same result.
How much does advantage help?
It depends on the number you need. The biggest gain, 25 percentage points, comes when you need an 11 on the die (50% becomes 75%), and the average d20 roll rises from 10.5 to 13.825.
Are the rolls fair?
Yes. Each die uses the browser's cryptographic random number generator with rejection sampling, so every face has the same chance.
Does a natural 20 always hit?
In 5th edition a natural 20 on an attack roll always hits and a natural 1 always misses, whatever the total. The odds shown here are for the total, so for an attack against a very high or very low AC remember those two faces.
Last updated: 2026-10-30