Dice odds
Dice Probability Calculator
Count the odds instead of guessing at them. Set up the dice you are actually rolling, ask for a total, and read the exact chance — including advantage, disadvantage, "roll 4d6 and drop the lowest" pools and flat modifiers. Then put a second roll next to it and see which one wins.
- d4 through d100, one to ten dice, any flat modifier
- At least, at most or exactly a target total
- Advantage, disadvantage and keep-the-highest pools
- Worked out in your browser — nothing you type is uploaded
Every total, and the odds of it
Totals run 5 to 15. "This or less" and "this or more" add up everything below and above each row.
| Total | Exactly | This or less | This or more |
|---|---|---|---|
| 5 | 2.78% | 2.78% | 100% |
| 6 | 5.56% | 8.33% | 97.2% |
| 7 | 8.33% | 16.7% | 91.7% |
| 8 | 11.1% | 27.8% | 83.3% |
| 9target | 13.9% | 41.7% | 72.2% |
| 10 | 16.7% | 58.3% | 58.3% |
| 11 | 13.9% | 72.2% | 41.7% |
| 12 | 11.1% | 83.3% | 27.8% |
| 13 | 8.33% | 91.7% | 16.7% |
| 14 | 5.56% | 97.2% | 8.33% |
| 15 | 2.78% | 100% | 2.78% |
Compare two rolls
Two weapons, two spells, a straight roll against advantage — put both pools in and read who wins, how often they tie, and what each one averages.
Roll A
2d6 + 3
roll 2 d6 dice and add them all up, then add 3
Average total 10.00
Roll B
Average total 8.50
2d6 + 3 beats 1d12 + 2: 58.3% (1 in 1.7)
| 2d6 + 3 wins | 58.3% — 1 in 1.7 |
|---|---|
| Tie (same total) | 8.10% — 1 in 12 |
| 1d12 + 2 wins | 33.6% — 1 in 3.0 |
| Average total, 2d6 + 3 | 10.00 |
| Average total, 1d12 + 2 | 8.50 |
| Average winning margin | 1.50 on average totals |
2d6 + 3 beats 1d12 + 2 in about 58.3% of rolls.
How to use it
- Build the pool. How many dice, which die, and whether you add everything together or keep only the best (or worst) of them. "Keep the highest die" on 2d20 is advantage; "keep the lowest" is disadvantage; "add up the highest 3" of 4d6 is the classic ability score roll.
- Type the total you care about. Modifiers go into the pool, not the target — a +5 attack against AC 15 is a target of 15, not 10. If you would rather work from the die face, set the modifier to 0 and the target to the number you need to see.
- Choose at least, at most or exactly. "At least" is the hit-or-miss question, "at most" is the save-or-threshold question, and "exactly" is for tables and random encounter keys that care about one number.
- Read the table underneath. Each row is one possible total with its own chance, plus running totals so you can see how the odds pile up as the number drops.
- Add a second roll to compare. Give Roll B its own dice and the page works out how often each one wins, how often they tie, and what each averages.
- Copy the numbers if you need them. The copy button hands you the whole thing as plain text for a session note or a group chat.
Worked examples
These are the questions I end up working out at the table most often. Every number below is calculated the same way the tool calculates yours.
| The question | The pool | The answer |
|---|---|---|
| My attack bonus is +5 and the monster is AC 15 — do I hit?You need a 10 or better on the die, so 11 of the 20 faces get there. | 1d20 + 5 | 55.0%chance of 15 or more |
| What are the odds of 9 or more on 2d6?Ten of the thirty-six combinations get there, and 7 stays the single likeliest total. | 2d6 | 27.8%chance of 9 or more |
| I have advantage on a DC 15 check — does that actually help?Two d20 keeping the higher one turns a 30% check into roughly a coin flip. | 2d20 keep the highest (advantage) | 51.0%chance of 15 or more |
| Rolling a character: how often does 4d6 drop the lowest give an 18?Twenty-one of the 1,296 outcomes leave three sixes standing. | 4d6 keep the highest 3 | 1.62%chance of 18 |
| How often does an 8d6 fireball roll 28 or better?The average is 28, so half the table lands at or above it. | 8d6 | 54.0%chance of 28 or more |
| Greatsword against greataxe — which one wins the damage race?Load the 2d6 + 3 preset on Roll A and 1d12 + 2 on Roll B. | 2d6 + 3 vs 1d12 + 2 | 58.3%Roll A wins |
What this calculator does not do
- It does not roll anything. Every number comes from counting the combinations, so there is no randomness and no sampling error — but it also will not tell you what your next throw will be.
- It does not roll for two players in turn. The comparison assumes both rolls happen independently, which is right for a damage race and wrong for anything where one result changes the other.
- It does not model exploding dice, re-rolls of specific faces, or "roll a d20 and then roll again on a 20". Those change the pool as you go, and this page only counts fixed pools.
- It does not track a whole turn. The odds of hitting, then wounding, then saving multiply together — work each step out here and multiply the percentages yourself.
- It works in browser floating point, so probabilities are exact in method but a hair off in the last decimal place or two. Round to a tenth of a percent and you are safe.
- It does not save, share or upload anything. Reload the page and it is back to the starting pool.
Questions I get about dice odds
What are the odds of rolling a 20 with advantage?
39 in 400, or 9.75%. Set the pool to 2d20 with "keep the highest" and ask for 20 or more: two dice miss a 20 in 19 x 19 = 361 of the 400 combinations, so 400 - 361 = 39 combinations hit.
What is the difference between "at least", "at most" and "exactly"?
"At least" adds up every total from your target upwards — the usual way to ask whether an attack hits. "At most" adds up everything below it, which is how you check a save or a threshold. "Exactly" is the single total on its own, which is what you want when a table or a random encounter keys off one number.
What does 4d6 drop the lowest actually average?
12.24, not 14. Rolling four dice and dropping the lowest pushes the average up to about 12.24 from the 10.5 you get on 3d6, and an 18 comes up 21 times in 1,296 — about 1.62%.
Can I use it for 2d6 board games like Monopoly or Catan?
Yes. Set 2d6 and ask for 7 or more and you get 58.33%, because 21 of the 36 combinations total 7 or better. Ask for 7 exactly and it drops to 16.67%, the single most likely total on two dice.
Does this simulate rolls, or work them out?
It works them out. Every total is counted by enumerating the combinations, so the answer is the same every time and there is no sampling error. Probabilities are held as browser floating-point numbers, so the display rounds at the last decimal place or two.
Why does the table stop at 41 rows for big pools?
A 10d100 pool has nearly a thousand possible totals and printing them all would bury the number you came for. Wide ranges show the 41 totals around your target, while the headline percentages, the average and the comparison always use the full range.
Is anything I type sent anywhere?
No. The pool, the target and the comparison are all calculated in your browser, and they are gone as soon as you close the tab. There is no account, no save and no upload.