D&D Dice Roller Calculator
Select your die type, how many dice to roll, and any flat modifier. The calculator shows your expected average, minimum, maximum, and the probability of meeting or beating any Difficulty Class target. Switch to Advantage or Disadvantage mode to see how rolling two d20s shifts the odds, or use Ability Score mode to simulate the classic 4d6 drop-lowest method.
How D&D dice work
Dungeons and Dragons uses a set of seven polyhedral dice: the d4, d6, d8, d10, d12, d20, and d100. Each is named for the number of faces it has, and each face is equally likely to land face-up, so every result in the range 1 to N has a 1-in-N probability. When you roll multiple dice of the same type, such as 3d6 for a fireball damage roll, you simply add all of the individual results together. The d20 is the centrepiece of the game: almost every meaningful action (attacking, casting a spell, persuading a guard, picking a lock) is resolved by rolling a d20, adding your relevant ability modifier and proficiency bonus, and comparing the total to a target number called the Difficulty Class.
Advantage, Disadvantage, and probability math
Advantage and Disadvantage are the two most important dice mechanics in D&D 5e. When you roll with Advantage, you roll two d20s and use the higher result. When you roll with Disadvantage, you use the lower result. The expected (average) result of a normal d20 roll is (1+20)/2 = 10.5. For Advantage the expected value is (2x20+1)/3 = 13.83, and for Disadvantage it is (20+2)/3 = 7.17. That two-point swing in each direction may sound small, but it has a dramatic effect on the probability of hitting a specific DC. For example, hitting DC 15 on a raw d20 has a 30% chance (6 out of 20 faces). With Advantage it rises to 51% (1 minus the probability both dice are below 15), and with Disadvantage it falls to just 9%. Knowing these numbers lets you decide when it is worth spending Inspiration or burning a spell slot to gain Advantage.
The 4d6 drop-lowest ability score method
The most common way to generate ability scores in D&D 5e is to roll four six-sided dice, discard the lowest result, and add the remaining three. The expected value of this method is approximately 12.24 per score, compared to 10.5 for a straight 3d6 roll or 10.5 for a flat choice. Rolling this six times and assigning the results to Strength, Dexterity, Constitution, Intelligence, Wisdom, and Charisma gives an expected total of around 73.5, compared to 72 for the Standard Array (15, 14, 13, 12, 10, 8). The random method offers a slightly higher ceiling but comes with variance: some players roll exceptionally high totals, others roll frustratingly low ones. Point-buy and the Standard Array eliminate variance and let you build your character concept from the start.
Using modifiers and the Difficulty Class system
Every d20 roll in D&D is modified by a relevant ability score modifier and, for proficient skills or attacks, a proficiency bonus that scales with character level (+2 at level 1 rising to +6 at level 17+). The Difficulty Class system defines how hard a task is: the Dungeon Master sets a DC (5 is very easy, 10 is easy, 15 is medium, 20 is hard, 25 is very hard, 30 is nearly impossible), and you succeed if your roll plus modifiers meets or exceeds that number. This calculator shows you exactly what percentage of rolls will meet any DC you specify, so you can judge at a glance whether attempting a risky action is worth it before your character commits.
D&D 5e standard polyhedral dice
| Die | Faces | Mean | Min-Max | Typical use |
|---|---|---|---|---|
| d4 | 4 | 2.5 | 1-4 | Dagger, magic missile, healing word |
| d6 | 6 | 3.5 | 1-6 | Short sword, fireball dice, hit die (rogue) |
| d8 | 8 | 4.5 | 1-8 | Longsword, cure wounds, hit die (cleric) |
| d10 | 10 | 5.5 | 1-10 | Heavy crossbow, hit die (fighter) |
| d12 | 12 | 6.5 | 1-12 | Greataxe, hit die (barbarian) |
| d20 | 20 | 10.5 | 1-20 | Attack rolls, ability checks, saving throws |
| d100 | 100 | 50.5 | 1-100 | Wild magic surge, percentage rolls |
The classic seven-piece D&D dice set and the typical uses for each die in gameplay.
Frequently asked questions
What dice do you need to play D&D?
The standard D&D dice set contains seven dice: one d4, one d6, one d8, two d10s (one marked 0-9 and one marked 00-90 for percentile rolls), one d12, and one d20. You can get by with a single set, but many players keep extra d6 dice handy for spells like Fireball that need to roll 8d6 at once. Digital roller tools like this one let you replicate any combination without a physical set.
What is the average roll on a d20?
The average result of a single d20 roll is 10.5, because every result from 1 to 20 is equally probable and the mean of a uniform 1-to-20 distribution is (1+20)/2 = 10.5. With Advantage (roll two d20s, take the higher) the average rises to about 13.83, and with Disadvantage (take the lower) it falls to about 7.17.
How does Advantage change my odds?
Advantage lets you roll two d20s and take the higher result. The probability of rolling at least k on a d20 with Advantage is 1 minus the probability that both dice are below k, which equals 1 - ((k-1)/20)^2. For example, hitting DC 15 normally requires rolling a 15 or higher: a 30% chance. With Advantage it becomes 1 - (14/20)^2 = 1 - 0.49 = 51%. The benefit is largest around the middle of the range and shrinks near the extremes.
What does 4d6 drop lowest mean?
The notation 4d6kh3 (keep highest 3) means you roll four six-sided dice and discard the lowest number. For example, rolling 3, 5, 2, 4 gives you 3 + 5 + 4 = 12 after dropping the 2. This method skews the distribution upward: the expected result is about 12.24 per roll, compared to 10.5 for a straight 3d6 sum.
What is a Difficulty Class (DC) in D&D?
A Difficulty Class is the number a character must meet or beat on a d20 roll plus relevant modifiers to succeed at a task. DC 10 is easy, DC 15 is moderate, DC 20 is hard, and DC 25 to 30 represents legendary difficulty. The Dungeon Master sets the DC; this calculator tells you the probability of success before you commit to rolling.
Is this a true random dice roller?
This page shows probability calculations based on exact math rather than a simulated roll. Every die type is a fair uniform distribution, so the probabilities shown are precise. For a live simulated roll where you click and see a random number, use the roll button on any of the popular online dice rollers linked in our sources section. Both approaches are equally valid: the math here tells you the odds before you roll.