D20 Dice Roller

Roll a d20 instantly for your tabletop game. Add a modifier, roll with advantage or disadvantage, or type any dice expression such as 2d6+3, 4d6 drop lowest or 1d20+5. Natural 20s and natural 1s are highlighted, every roll is kept in the history, and the randomness comes from your browser’s cryptographic generator.

How to use the dice roller

1. Press “Roll d20” for a single twenty-sided die. Add a modifier — your ability or skill bonus — in the box.
2. Choose advantage (roll two d20s and keep the higher) or disadvantage (keep the lower) when your game calls for it.
3. Use the buttons for d4, d6, d8, d10, d12 and d100.
4. Type any dice expression, such as 2d6+3 for a weapon’s damage, and press “Roll expression”.
5. Roll six ability scores with the classic 4d6-drop-lowest method in one click.
6. Check the history to see previous rolls.

Natural 20s appear in green and natural 1s in red, since many games treat them as critical successes or failures.

Dice notation explained

Probabilities on a d20

Each face of a fair d20 has a 1 in 20 (5%) chance. Rolling a 10 or higher happens 55% of the time; 15 or higher, 30%. Advantage changes this a lot: the chance of at least one 20 on two dice is 9.75%, and the chance of getting 10 or higher rises from 55% to about 80%. Disadvantage has the opposite effect, dropping the chance of 10 or higher to about 30%. Advantage is roughly worth a +3 to +5 bonus in the middle of the range, which is why games treat it as powerful.

Common dice and what they are used for

The average of a die is (sides + 1) ÷ 2, so 2d6 averages 7 — the most common result on two six-sided dice.

Is the roller fair?

Each roll uses the browser’s cryptographically secure random number generator and maps it to a die face without bias. Physical dice can be slightly unbalanced by manufacturing flaws, so a good digital roller is at least as fair as real dice. Like real dice, it has no memory: rolling three 1s in a row does not make a 20 more likely next time.

Worked example

A fighter with a +5 attack bonus attacks with advantage. They set the modifier to 5, choose Advantage and roll: the dice show 7 and 16, the roller keeps 16 and reports 21. The attack hits, so they type 1d8+3 for a longsword’s damage and roll a 6, for 9 damage. When the next character levels up, the group uses “Roll stats” to generate six ability scores with 4d6 drop lowest.

Critical hits and fumbles

Many tabletop role-playing games treat a natural 20 — the die showing 20 before modifiers — as an automatic success or critical hit, and a natural 1 as an automatic miss or fumble on attack rolls. Rules differ between games and editions, and many groups have house rules, so the roller simply highlights naturals and leaves the interpretation to your table. On a single d20 each has a 5% chance; with advantage, the chance of a natural 20 rises to 9.75% and of a natural 1 falls to 0.25%.

Digital vs physical dice

Physical dice are part of the fun for many players, and a digital roller is a handy backup when dice are missing, for online games, or when you need to roll many dice at once — 8d6 for a big spell, or dozens of damage dice. The expression box handles large pools instantly and shows every individual die, so players can still see what was rolled. Some groups use a shared screen so the whole table sees the history.

Beyond fantasy games

• Board games that use dice when the physical ones go missing.
• Classroom probability experiments — roll 100 times and compare with theory.
• Random decisions and prompts for writing or art.
• Solo games and journaling games that use random tables.

Privacy

Rolls happen in your browser and are not recorded anywhere except the on-page history, which clears when you close the page.