What Is an Online Dice Roller
An online dice roller generates integer faces for virtual dice. Choose how many dice to roll and how many sides each die has, then add an optional modifier to the pool subtotal. This page supports familiar polyhedral dice such as D4, D6, D8, D10, D12, D20, and D100 plus custom dice from 2 to 1,000 sides.
The result is more than one total. It keeps every retained die visible, shows both attempts when a keep rule is selected, counts successes against a chosen threshold, summarizes observed faces, and separates a single random outcome from long-run probability measures.
How to Use the Dice Roller
Select a standard die preset or enter a custom side count. Set the number of dice, a whole-number modifier for the final total, and the face that counts as a success. Normal mode rolls one pool. Keep-higher and keep-lower modes roll two complete pools with identical settings and retain one total.
Select Roll dice for a fresh independent result. Read the retained dice and total before the statistical context. The history list records recent rolls only for the current page session and can be cleared without changing the calculator inputs.
- Choose D4, D6, D8, D10, D12, D20, D100, or enter custom sides.
- Enter between 1 and 100 dice and an optional whole-number total modifier.
- Choose normal, keep-higher, or keep-lower mode.
- Set a success threshold from 1 through the selected number of sides.
- Roll, inspect both attempts when shown, and use history to compare recent outcomes.
Reading NdS and Modifier Dice Notation
Common dice notation writes the number of dice before d and the sides per die after it. The expression 2d6 means roll two six-sided dice. The expression 4d8+3 means roll four eight-sided dice, add their faces, then add 3 once to the pool total. A negative modifier such as 1d20-2 lowers the total but never changes the face rolled.
This page displays simple NdS plus or minus modifier notation. It does not parse a free-form expression or implement exploding, reroll, drop, compound, or chained arithmetic syntax. The visible mode label explains the separate two-pool keep rule.
Normal, Keep-Higher, and Keep-Lower Modes
Normal mode generates one dice pool and uses its modified total. Keep-higher generates two complete pools with the same dice, sides, and modifier, then retains the larger total. Keep-lower retains the smaller total. Both attempts remain visible so the discarded outcome is never hidden.
For a familiar one-die d20 check, choose 1 die and 20 sides. The two-pool modes can resemble advantage or disadvantage when a game uses that rule, but game systems define their own tie handling, modifiers, eligible checks, and special effects. This calculator deliberately labels the mechanical operation instead of claiming universal rule compatibility.
How Browser Randomness Produces Each Die Face
Each face starts with crypto.getRandomValues(), the browser Web Crypto source for cryptographically strong random values. The implementation does not use Math.random. It then applies rejection sampling: values in the small uneven remainder above the largest evenly divisible range are discarded and redrawn before mapping the accepted value to a die face.
That rejection step avoids modulo bias when the random source range is not exactly divisible by the number of die faces. Every accepted face from 1 through S therefore has the same theoretical probability under the browser source. A result cannot be reconstructed later because this tool does not expose or store an auditable seed.
Possible Totals, Expected Value, and Spread
For N fair S-sided dice, the smallest subtotal is N and the largest is N times S. The expected face of one die is (S + 1) / 2, so the expected subtotal of a normal attempt is N times (S + 1) / 2. Add the modifier once to obtain the expected modified total. Expected value is a long-run average, not a prediction for the next roll.
The theoretical standard deviation of the normal pool total is the square root of N times (S squared - 1) / 12. More dice increase the possible range but make the average per die tend to cluster more consistently around the midpoint over repeated independent trials. Keep-higher and keep-lower selection changes the retained-total distribution, so the page labels its displayed expected value as the expectation for one normal attempt.
Success Thresholds and Dice Pools
Some games and classroom exercises count each die at or above a target as one success. If a fair S-sided die succeeds on T through S, the chance per die is (S - T + 1) / S. The expected number of successes in one independent pool is the number of dice multiplied by that probability.
The chance of at least one success in one pool is 1 minus the chance that every die fails. The result reports these one-attempt figures beside the observed success count. A keep-higher or keep-lower rule chooses by total, not by success count, so the retained pool is not guaranteed to contain the most or fewest successes.
Dice Roller Examples
These examples separate the dice pool from the modifier and explain what the mode retains. Actual faces and totals change every time Roll dice is selected.
| Setup | Possible normal total | Expected normal total | Typical use |
|---|---|---|---|
| 2d6 | 2 to 12 | 7 | Board-game movement or a two-dice sum |
| 4d6+2 | 6 to 26 | 16 | A multi-die pool with one total modifier |
| 1d20+5 | 6 to 25 | 15.5 | A d20 check with a fixed bonus |
| 1d100 | 1 to 100 | 50.5 | Percentile-style random result |
| 6d10, target 8 | 6 to 60 | 33 total; 1.8 successes | Count each 8, 9, or 10 as a success |
Standard Dice Presets at a Glance
The preset row changes only the side count. Dice count, modifier, mode, and threshold remain editable so the same interface can cover one die, a large pool, or a custom classroom experiment.
| Preset | Face range | Expected face | Common context |
|---|---|---|---|
| D4 | 1-4 | 2.5 | Small polyhedral result |
| D6 | 1-6 | 3.5 | Board games and familiar cube dice |
| D8 | 1-8 | 4.5 | Tabletop role-playing games |
| D10 | 1-10 | 5.5 | Decimal or dice-pool systems |
| D12 | 1-12 | 6.5 | Tabletop role-playing games |
| D20 | 1-20 | 10.5 | D20 checks and saves |
| D100 | 1-100 | 50.5 | Percentile rolls |
Dice Roller Features
The workspace prioritizes fast rolling while preserving the information needed to audit a result. Controls, retained faces, probability context, frequency details, export actions, and recent history stay on one responsive page.
- One-click D4, D6, D8, D10, D12, D20, and D100 presets.
- One to 100 dice with two to 1,000 sides per die.
- Whole-number positive, zero, or negative total modifier.
- Normal, keep-higher, and keep-lower pool modes with both attempts visible.
- Configurable per-die success threshold and theoretical success context.
- Minimum, maximum, expected total, standard deviation, median, mode, and frequency table.
- Current-session roll history, copy action, and downloadable result and table PDFs.
Benefits of a Transparent Virtual Dice Roller
A transparent roller removes arithmetic from large pools without hiding the individual faces. Players can verify the subtotal and modifier, teachers can discuss expected value beside an observed outcome, and facilitators can generate a quick random choice without installing an app or creating an account.
The distinction between observed and theoretical results is equally important. One unusual roll is possible and does not demonstrate bias. Frequency and average become meaningful evidence only across an appropriately designed collection of independent trials.
Common Dice Roller Use Cases
Use the roller for casual, educational, and tabletop tasks where a browser-generated result is acceptable. Check the governing game or activity rules before choosing the dice expression or keep mode.
- Roll attacks, checks, damage, healing, or encounter values in tabletop games.
- Replace missing physical dice during a board game.
- Demonstrate probability, expected value, frequency, and sampling in class.
- Count target successes in a custom dice pool.
- Generate a casual random prompt, order, or choice with numbered options.
- Compare a normal pool with two-attempt keep-higher or keep-lower outcomes.
Accuracy, Fairness, Privacy, and Limits
The arithmetic after each accepted face is deterministic and can be checked from the visible dice. Web Crypto and rejection sampling are appropriate for an unbiased casual browser roll, but this page is not a certified random-number service. It has no independent draw witness, tamper-evident log, public seed, reproducible seed, or external audit trail.
Use an authorized, documented system when money, prizes, regulated gambling, security, legal selection, research protocol, or a contest rule requires certified or reproducible randomness. Recent history exists only in the current React page session and is not saved as a user account record.
- Verify dice count, side count, modifier, mode, and success threshold before rolling.
- Remember that the modifier changes only the total, not individual faces or successes.
- Treat expected value as a long-run mean, never a promised next result.
- Do not infer fairness from one roll or a very small sample.
- Use the official rules for any game-specific advantage, disadvantage, reroll, or keep mechanic.
Helpful Dice Randomness and Probability References
These references document the browser randomness source, expected-value concepts, and common dice-notation conventions. The notation project is a technical reference, not a universal tabletop rules authority.