D20 Roller
Roll a virtual d20 — an icosahedron with twenty triangular faces — the signature die of the d20 System. Every face lands with an equal 1-in-20 probability and an average roll of 10.5, generated with cryptographic randomness in your browser. The d20 is the most famous die in gaming: an icosahedron whose flat 5%-per-face spread makes every roll a clean probability step. Quality d20s are checked for balance because even small moulding bubbles skew a die whose faces are all meant to be equally likely.
D20 Roller reference last updated · reference source
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Dated static reference; no live data is fetched. Verify current source values and assumptions before relying on results.
What this tool does
Roll a virtual d20 — an icosahedron with twenty triangular faces — the signature die of the d20 System. Every face lands with an equal 1-in-20 probability and an average roll of 10.5, generated with cryptographic randomness in your browser. The d20 is the most famous die in gaming: an icosahedron whose flat 5%-per-face spread makes every roll a clean probability step. Quality d20s are checked for balance because even small moulding bubbles skew a die whose faces are all meant to be equally likely.
How to use the D20 Roller
- Check Sides per die: 20.
- Check Dice count: 1.
- Review the D20 Roller result and its exact-value comparison table.
- Verify assumptions before applying the result.
Formula
each die is a uniform integer from 1 through sides, using Web Crypto
- sides
- Sides per die
- count
- Dice count
Independent virtual dice. Generate again to reroll.
Worked example
D20 Roller: Sides per die = 20; Dice count = 1. Roll a virtual d20 — an icosahedron with twenty triangular faces — the signature die of the d20 System. Every face lands with an equal 1-in-20 probability and an average roll of 10.5, generated with cryptographic randomness in your browser. The d20 is the most famous die in gaming: an icosahedron whose flat 5%-per-face spread makes every roll a clean probability step. Quality d20s are checked for balance because even small moulding bubbles skew a die whose faces are all meant to be equally likely.
Inputs
- Sides per die20
- Dice count1
Result
- Total13
- Rolls13
- Expected total (average over many rolls)10.5
- Minimum possible total1
- Maximum possible total20
- Chance of the maximum total5%
- Chance each single die shows its top face5%
D20 quick odds
| Question | Answer |
|---|---|
| Average roll | 10.5 |
| Chance of any single face | 1 in 20 (5%) |
| Chance of rolling the maximum (20) | 1 in 20 |
| Chance of rolling above the average (over 10.5) | 10 in 20 (50%) |
| Faces | 20 |
Results explained
- Total
- The sum of the independent d20 rolls shown, each a uniform integer from 1 to 20.
- Rolls
- The individual die results in the order rolled.
- Expected total (average over many rolls)
- Dice count × 10.5, the theoretical average for a d20.
- Chance of the maximum total
- The probability that every die in the roll shows 20 at once: (1/20)^count.
Frequently asked questions
The entire d20 System is named for it: Dungeons & Dragons and Pathfinder resolve attacks, saving throws and ability checks with a single d20, where a natural 20 is an automatic critical success and a natural 1 an automatic critical failure on attacks. Board games like Gloomhaven also use d20-based modifier decks inspired by it.
(20 + 1) ÷ 2 = 10.5. Every face from 1 to 20 is equally likely, so the long-run average sits exactly halfway between the minimum and maximum.
Exactly 1 in 20, or 5%, on a single die. With two dice both showing 20 the chance drops to 1 in 400 (0.25%).
Yes. Rolls come from the Web Crypto API with rejection sampling, so no face is favoured by modulo bias, and nothing is weighted, seeded from the clock or influenced by previous rolls.
A d20 has no memory: after three natural 20s in a row, the chance of a fourth is still exactly 5% — the full run of four had a probability of just 0.000625% before the first roll.
Yes — raise the dice count (gamers write that as 2d20, 3d20 and so on). Totals then follow a bell curve centred on 10.5 per die: extremes get rarer as you add dice, which is why multi-dice rolls feel more predictable than a single big die.