Free TTRPG dice probability calculator. Build a pool (e.g. 3d6 + 1d4 + 2) and a target difficulty; outputs probability of hitting the target, mean, distribution histogram, and supports advantage / disadvantage and exploding dice mechanics.
Use when designing custom monsters, homebrew rules, or just sanity-checking your party's odds. Especially valuable for indie game designers balancing core mechanics.
AnyDice is the legacy reference and supports far more — but its UI is intimidating. This tool covers 90% of common cases without learning a scripting language.
The probability mass function (PMF) of the sum of N dice is computed by convolution. Modifiers shift the PMF; advantage/disadvantage recomputes from two independent rolls.
Success chance is the cumulative probability of the sum (plus modifier) meeting or exceeding the target.
The distribution chart shows every possible total, with bars above the target highlighted in green.
Yes — roll twice and take highest/lowest. The PMF is recomputed accordingly.
Not yet — it's on the list. Use a standard pool with a slightly larger die size as a rough approximation.
The mean is the long-run average total you would roll, useful for balancing damage or setting target difficulties. For a single fair die it sits halfway between the lowest and highest face, such as 3.5 on a d6.
Adding several dice together makes middle totals far more likely than extreme highs or lows, because many die combinations produce a middling sum but only one produces the maximum. This clustering is why 3d6 feels more consistent than a single d18.
ইনপুট
3d6 + 5 vs target 15, standard roll.
আউটপুট
78.2% success. Mean total: 15.5.
3d6 has mean 10.5, range 3–18; adding +5 gives mean 15.5, range 8–23. To beat 15 you need a base roll ≥ 10, which the cumulative distribution puts at ~78%.
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