Advantage/Disadvantage Roller

What this generator does

Rolls two dice of whatever size you choose and takes either the higher or the lower, the advantage and disadvantage mechanic most associated with the d20 but built here to work for any die size. Showing both dice matters: knowing what you avoided is part of the moment.

How to use this tool

1. Choose the number of sides per die.
2. Choose advantage or disadvantage.
3. Roll to see both results and the one that counts.

Understanding the controls

Sides per die

From 2 to 100. The mechanic works the same for any size — d20 is the common case, but nothing is hard-coded to it.

Mode

Advantage keeps the higher of the two, disadvantage the lower. On a d20 advantage shifts the average result up by about 3.3, from 10.5 to roughly 13.8; disadvantage moves it down by about the same, to roughly 7.2.

Worked examples

A d20 check with advantage

Rolling with advantage on a d20, both dice are shown — say a 6 and a 14 — and 14 counts. Over many rolls the average result with advantage is about 13.8 rather than the flat 10.5 of a single die.

Common use cases

• Ability checks with advantage or disadvantage
• Any game mechanic using roll-two-keep-one

How this generator works

Two independent dice of the size you choose are rolled from your browser's Web Crypto generator, and the higher (advantage) or lower (disadvantage) of the two is taken as the result. Both rolls are always shown, not just the one that counts. The shift this produces is exact and can be worked out from the two rolls' joint distribution: for a d20, the average of the higher of two rolls is 13.825 and the average of the lower is 7.175 — each about 3.3 away from the flat 10.5 average of a single die, and the two shifts are always equal and opposite because the higher and lower roll between them always add up to the same total as the two original dice.

Limitations and good to know

• Only two dice are rolled and compared — for keeping several dice out of a larger pool, use the keep-highest or keep-lowest dice roller instead.
• The shift is not the same fraction of the range on every die size: 0.625 on a d4, about 21% of its range of three, against 3.325 on a d20, 17.5% of its range of nineteen.

Frequently asked questions

Does advantage double my chance of a good roll?

No — it shifts the average up (about 3.3 higher on a d20) rather than doubling anything. It helps most at the extremes: the chance of rolling the maximum roughly doubles, but the chance of an already-middling roll barely changes.