What a d2 is for
- A coin flip. Call 1 for heads and 2 for tails, or the other way round, before the roll.
- Yes or no. Does the guard notice? Is the bridge still standing? When nobody at the table knows, let the coin decide.
- Splitting two ways. Which of two doors, which of two players, which half of the party the ogre goes for.
- 1d2 in the rules. Older editions and Pathfinder use 1d2 for the smallest damage, such as a Small character's unarmed strike.
Rolling a d2 without one
Nobody sells a two-sided die, so the rules have always faked it. The usual way is to roll any die and call odd 1 and even 2. This page skips that and flips a real coin with a 1 and a 2 on it.
Is it fair?
Each face comes up one time in two. The number comes from your browser's cryptographic random generator, not from how the coin tumbles. Flip ten at once and count them: a streak of five or more the same, all 1s or all 2s, turns up about one time in five, far more often than it feels like it should.
Your odds on a d2
Waiting for a 2? The chance of at least one climbs fast:
| Rolls | At least one 2 |
|---|---|
| 1 | 50% |
| 2 | 75% |
| 3 | 87.5% |
| 4 | 93.8% |
| 5 | 96.9% |
| 6 | 98.4% |
Ten coins at once, counting the 2s:
| 2s | Chance | Meaning |
|---|---|---|
| 5 | 24.6% | The most likely count, and still under 1 in 4 |
| 4 to 6 | 65.6% | About two times in three |
| 0 or 10 | 0.2% | All the same: 1 in 512 |
The dice calculator works out any roll, the d3 sits one size up and the d4 above that.
Questions
What does 1d2 mean?
One two-sided die, a roll of 1 or 2. The number in front is how many, so 2d2 is two of them added together (2 to 4) and 1d2 + 1 gives 2 or 3. The Dice Notation Guide covers the rest.
How do I roll a d2 without one?
Roll any die with an even number of sides and call odd 1 and even 2. A d6, d10 or d20 all work and all are perfectly fair. A coin works too: pick which side is 1 before you flip.
Is a d2 the same as a coin flip?
Yes. Both have two outcomes, each exactly 1 in 2. The only difference is the label: a d2 reads 1 or 2, a coin reads heads or tails.
What is the average roll on a d2?
Exactly 1.5. Each extra d2 adds 1.5, so 2d2 averages 3 and 4d2 averages 6.
Do real d2 dice exist?
Yes, but they are rare: thick coins with a number on each face, or d6s marked 1, 1, 1, 2, 2, 2. Most tables just use a d6 or a coin.
Is this d2 roller random and fair?
Yes. Each roll comes from your browser's cryptographic random number generator, so 1 and 2 are each exactly 1 in 2. Roll up to 20 at once and add a modifier.