Table probability reference
Read the odds before the dice land.
A d20 is flat, two d6 form a curve, and a d100 maps directly to percentages. Use the table that matches the roll instead of treating every total the same way.
D20 thresholds
On a fair d20, each face has a 5% chance. To find the chance of meeting a target without a modifier, count the successful faces from the target through 20.
| Target on the die | Successful faces | Chance |
|---|---|---|
| 5 or higher | 16 of 20 | 80% |
| 10 or higher | 11 of 20 | 55% |
| 15 or higher | 6 of 20 | 30% |
| Natural 20 | 1 of 20 | 5% |
A modifier changes the face needed, not the die itself. Against difficulty 15, a +5 modifier means a natural 10 or higher succeeds: 11 faces out of 20, or 55%. Advantage, disadvantage, rerolls and special game rules need a different calculation.
2d6 total distribution
Two six-sided dice produce 36 equally likely face pairs, but the totals are not equally likely. Six pairs total 7; only one pair totals 2 and one totals 12.
| Total | Ways out of 36 | Chance |
|---|---|---|
| 2 | 1 | 2.78% |
| 3 | 2 | 5.56% |
| 4 | 3 | 8.33% |
| 5 | 4 | 11.11% |
| 6 | 5 | 13.89% |
| 7 | 6 | 16.67% |
| 8 | 5 | 13.89% |
| 9 | 4 | 11.11% |
| 10 | 3 | 8.33% |
| 11 | 2 | 5.56% |
| 12 | 1 | 2.78% |
Use 2d6 when a game intentionally makes middle totals more common than extremes. The roller shows both dice and their sum; the game determines what that total means.
D100 percentage rolls
A uniform d100 gives every integer from 1 to 100 a 1% chance. In a “roll equal to or under” check, a target of 73 succeeds on 73 results. Rolling exactly 100 remains a 1% event.
The tool supports one physical 100-sided die and two-d10 percentile mode. Both cover 1–100, but the visible dice are read differently. The d100 guide explains 00 + 0 = 100, 00 + 7 = 7 and when to choose each mode.
What these numbers assume
- Each face is equally likely within the selected result path.
- Each die is treated as an independent roll.
- No reroll, keep-high, keep-low or exploding-die rule has been applied.
- Modifiers change totals or thresholds; they do not change a fair die's face probabilities.
For accepted input formats, read the dice notation guide. For the physical and fallback result paths, read How It Works.