Dice stats (odds & distribution) + PNG sharing

Expression & method

Dice expression

Supports NdS +/- K (e.g., 2d6+3, d20, d%). Up to 200 dice and sides 2–1000. Uppercase D and spaces are normalized.

Mode

In Auto, expressions with a small number of possible totals use an exact calculation (Exact), and wide-range expressions use a simulation (Sim). If you are unsure, leaving it on Auto is recommended.

Sim iterations

Higher counts give smoother results but take more time. Applies to Sim mode only.

Presets

1) Enter or tap a preset. Try 2d6+3 or d20+5.
2) Pick a method. Auto is recommended. Exact (exact calculation) works well for small expressions, and Sim (simulation) for larger or DC-planning cases.
3) Read the result. Success odds, mean/SD, modes, and histogram update instantly.

Success condition & odds

Condition

k

Success probability

P(total ≥ 10) = —

Sim mode shows an estimate. The parser normalizes unsupported inputs. Here, total means the sum of all dice.

Key stats & modes

Minimum

—

Smallest reachable total

Maximum

—

Largest reachable total

Mean

—

Expected value (Exact) or sample mean (Sim)

Standard deviation

—

How much the totals vary

Modes (top 3)

Distribution (histogram)

When the total range is wide, values are grouped automatically into up to 60 bars.

Minimum and maximum totals are labeled automatically. A numeric summary is shown below so you can read the distribution without relying only on the chart.

Value / range	Probability	Note

History

Dice probability workflow

Use this page to parse dice notation, compute outcome probabilities, compare success thresholds, and share a stable result card.

How it works

Enter notation such as 2d6+3, d20, or d%. Auto mode uses exact enumeration when the outcome space is small enough and simulation when the expression is too wide.

When to use

Use it for tabletop DC planning, teaching probability distributions, checking house-rule modifiers, or comparing advantage from a bonus before a session.

Common mistakes to avoid

Forgetting that d% means a percentile die rather than a percent field.
Comparing a target number without choosing whether success means at least, at most, or exactly that value.
Reading a simulated tail probability as exact when the expression required random trials.
Sharing a screenshot without the notation and mode that produced it.

Result workflow

Enter notation, choose Auto, Exact, or Sim, set the success target if needed, then use the histogram, text summary, PNG export, or URL share depending on how the result will be discussed.

How to use & FAQ

Great for DC planning: switch Auto/Exact/Sim, compare odds and spread, and share a clean result card with your group.

Which dice notation is supported?

The parser accepts NdS +/- K such as 2d6+3, d20, or d%. You can roll up to 200 dice with sides from 2 to 1000. It also normalizes uppercase D and extra spaces.

How do Exact and Sim switch?

Auto uses Exact when total dice are small and the support size is within 6000; otherwise it switches to Sim. Even in Exact mode, very wide expressions fall back to Sim. All calculations run entirely in your browser.

When should I force Exact or Sim?

Use Exact for small dice pools when you need reproducible probabilities. Use Sim for large expressions where exact enumeration would be too slow.

How do I check a DC threshold?

Enter the dice notation, set the target value, and choose whether success is at least, at most, or exactly that number.

Can I share the result without rerolling?

Yes. The share URL stores the notation and settings, while the PNG export captures the current histogram and summary.