D20 Dice Roller

How to use

1. The d20 chip is pre-selected. Leave Count at 1 for a normal check.
2. Type your bonus into Modifier: attack bonus, save bonus, or skill modifier (negative numbers work).
3. For advantage type d20adv in the formula field, for disadvantage d20dis. You can still add a modifier: d20adv+5.
4. Hit Roll. The total is shown big; the detail line shows the natural roll(s), so a natural 20 or natural 1 is obvious.
5. The history keeps your last rolls in order — handy when the DM asks "what did you roll last turn?"

The d20 in D&D 5e: what one die decides

Almost everything in fifth edition is a d20 test: attack rolls, saving throws and ability checks. You roll the die, add a modifier (ability score bonus, proficiency, magic items) and compare with a target number — the Armor Class of the monster or the Difficulty Class of the task. Meet or beat it and you succeed.

Each face is a flat 5%, so the modifier matters more than people think: a +5 turns a 55% chance to hit AC 15 into 80%. The average roll is 10.5, which is why a "DC 15" task with no bonus fails more often than it succeeds.

Advantage and disadvantage

Advantage means you roll two d20 and keep the higher; disadvantage means you keep the lower. They do not stack — two sources of advantage are still one extra die — and if you have both at once they cancel out and you roll a single d20. The tool shows both dice in the detail line, so you can see the discarded one.

Statistically advantage is worth about +5 on rolls near the middle (needing 10–12) and less at the extremes: it raises the average from 10.5 to 13.825, while disadvantage drops it to 7.175. A natural 20 with advantage happens 9.75% of the time instead of 5%; with disadvantage it is 1 in 400.

Natural 20 and natural 1

A natural 20 is the die itself showing 20, before modifiers. On an attack roll it always hits, whatever the AC, and it is a critical hit: you roll the attack's damage dice twice (the modifiers are added once). A natural 1 on an attack roll always misses, even if your bonus would beat the AC.

In the 2014 rules only attack rolls have automatic success and failure; ability checks and saves just use the total. The 2024 revision of the Player's Handbook extends automatic success on a 20 and automatic failure on a 1 to every d20 test — check which version your table plays. Death saving throws are special in both: a 20 brings you back with 1 hit point, a 1 counts as two failures.

Who uses a d20 roller

• Online D&D groups that play over Discord without a virtual tabletop — one tab, shared screen, rolls everyone can see.
• Pathfinder 2e and other d20 systems — same die, the formula field handles the modifiers.
• Dungeon Masters rolling for a dozen goblins: set Count to 12 and every attack roll shows separately.
• Streamers and TikTok "roll a d20 to decide" formats — the big number reads well on camera.
• Teachers using the table above to show why advantage is not "double the chance".

What makes ours different

• Opens with the d20 ready; one tap to roll instead of picking a die every time.
• Advantage and disadvantage are real double rolls with both dice visible, not a hidden reroll.
• Natural rolls are shown separately from the total, so crits and fumbles are never in doubt.
• Cryptographic randomness (crypto.getRandomValues with rejection sampling), the same engine as our full dice roller.
• Roll history, modifiers, up to 100 d20 at once, no account, no ads on top of the button.

Privacy

Every roll happens in your browser. Nothing is sent to a server, there is no account and no log of your rolls anywhere except the history strip on your own screen.

FAQ