Dice Probability Lab
Computes the exact probability distribution of any dice expression — no simulation, every combination counted. Supports modifiers, keep/drop rules (4d6 keep highest 3, advantage 2d20kh1), the mean, standard deviation and median, "at least X" probabilities, and a side-by-side comparison of two expressions.
Runs 100% in your browser — nothing you generate leaves your device.
Read the full guide to this tool
Notes
- Notation: NdS rolls N dice with S sides; +/− chains terms; kh/kl keeps the highest or lowest dice, dh/dl drops them (4d6kh3 = 4d6dl1); d% is a d100.
- Every curve is computed by exact convolution and dynamic programming, so probabilities are precise to the last digit even for one-in-a-billion tails.
- Advantage (2d20kh1) shifts the mean from 10.5 to about 13.8 and lifts the chance of rolling 20 from 5% to 9.75%.
- Everything runs locally in your browser; nothing you enter or generate is sent to any server.
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