How is the probability calculated?

The tool uses dynamic programming (convolution) to count all possible combinations that produce each sum, then divides by the total number of outcomes. This gives exact probabilities, not estimates.

What does "at least X" mean?

"At least X" is the probability that your total roll (including modifier) is greater than or equal to X. This is the most useful metric for beating a target DC in RPGs.

Why does 2d6 feel more consistent than 1d12?

2d6 has a bell-curve distribution centered on 7, while 1d12 is flat (each value equally likely). The bell curve means mid-range results are far more probable with 2d6.

What is the range of supported dice?

Standard dice (d4, d6, d8, d10, d12, d20) plus any custom die from d2 to d100. You can roll 1 to 10 of them at once.

Does the modifier affect probabilities?

Yes. The modifier shifts the entire distribution up or down. For example, rolling 1d20+5 means all results are 5 higher, so hitting DC 15 requires only a roll of 10 or better.

Dice Probability Calculator

Name: Dice Probability Calculator
Availability: InStock
Author: Nham Vu

Select dice type and count, then see the full probability distribution and odds for any target sum.

Dice Configuration

Die Type

Number of Dice

Modifier (±)

Target Sum Lookup

Enter a target value to see the probability of rolling exactly that sum or at least that sum.

Target Sum

Configure your dice and click Calculate

Probability distribution will appear here

Summary

Select dice type and count, then see the full probability distribution and odds for any target sum.

How it works

Select a die type (d4, d6, d8, d10, d12, d20, or enter custom sides).
Set the number of dice to roll (1 to 10).
Optionally enter a flat modifier to add to the roll total.
Click Calculate to compute the full probability distribution.
Use the Target Sum inputs to see the exact probability of rolling at least or exactly a given value.

Use cases

Find the odds of hitting a target difficulty class (DC) in D&D 5e.
Compare attack success rates across different dice combinations.
Optimize damage output in tabletop RPGs by evaluating dice pools.
Understand the probability curve of 2d6 vs 1d12 for game design.
Calculate the chance of rolling a natural 20 on multiple d20s.
Evaluate loot drop mechanics involving custom-sided dice.
Plan strategy in board games by knowing the likelihood of outcomes.
Teach probability concepts using familiar dice examples.

Frequently Asked Questions

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Last updated: 2026-05-29 · Reviewed by Nham Vu