Dice Roller

This online dice roller simulates any standard polyhedral die used in tabletop roleplaying games, board games, and probability exercises. Pick a die type, set how many to roll, add an optional modifier, and get an instant virtual dice result. Whether you need a quick d20 for a D&D attack roll, 2d6 for damage, or 4d6 drop lowest for ability scores, this dnd dice roller handles the full classic set: d4, d6, d8, d10, d12, d20, and d100.

1. Select the die type (d4, d6, d8, d10, d12, d20, or d100/percentile). The d20 roller is the workhorse of D&D 5e and Pathfinder for attack rolls, saves, and checks. The d6 roll is the common choice for damage dice and most board games. The d100 doubles as a percentile roller for Call of Cthulhu and critical hit tables.
2. Choose the number of dice from 1 to 20. Rolling multiple dice at once is how you handle pool-based systems like Shadowrun (d6 pool), World of Darkness (d10 pool), or damage expressions like 8d6 fireball.
3. Set a modifier (optional). The modifier is added to or subtracted from the total after the dice are summed. A 1d20+5 for an attack means roll one twenty-sided die and add 5 from your Strength bonus and proficiency.
4. Handle drop-lowest or drop-highest manually. For the classic 4d6 drop lowest ability-score method, roll 4d6, then ignore the smallest face shown in the individual dice panel and sum the remaining three.
5. Handle advantage and disadvantage manually. For D&D 5e advantage, roll 1d20 twice and keep the higher. For disadvantage, keep the lower. Use the roll history panel on the right to compare the two results.
6. Click Roll. Each individual die is shown, with the maximum face highlighted green and a natural 1 highlighted red so you can spot crits and fumbles at a glance.

The random dice engine uses your browser's built-in random number generator, so results are instant and there is no server call. Every roll and its modifier are logged to a short history so you can re-check the last several outcomes without writing anything down at the table.

Tabletop gaming uses a compact shorthand called dice notation to describe exactly which dice to roll and what to do with them. Learning the notation takes about a minute and unlocks every rulebook, spell description, and monster stat block ever printed. The same math also tells you which outcomes are likely and which are long shots, so you can read a damage expression or a skill check the way a probability textbook reads a distribution.

Standard Dice Notation (XdY+Z)

The basic pattern is XdY+Z, which means "roll X dice that each have Y sides, sum them, then add Z as a flat modifier." A few worked examples:

• 3d6 = roll three six-sided dice and sum them. Range 3 to 18. Used for classic D&D ability score generation and GURPS skill rolls.
• 1d20+5 = roll one twenty-sided die and add 5. Range 6 to 25. This is a standard D&D 5e attack roll at low level.
• 4d6 drop lowest = roll four six-sided dice, discard the smallest face, sum the remaining three. Range 3 to 18, but weighted toward higher numbers. This is the classic D&D ability score method.
• 2d10 or 1d100 = percentile dice. Both give a range of 1 to 100 (or 0 to 99 on some tables).
• 8d6 = eight six-sided dice, summed. A 5th-level fireball in D&D 5e. Range 8 to 48, expected value 28.

Expected Value of a Dice Roll

The expected value (the long-run average) of rolling X dice with Y sides each is:

E[XdY] = X × (Y + 1) ÷ 2

E[1d6]  = 1 × 7 ÷ 2 = 3.5
E[2d6]  = 2 × 7 ÷ 2 = 7
E[3d6]  = 3 × 7 ÷ 2 = 10.5
E[1d20] = 1 × 21 ÷ 2 = 10.5
E[4d6]  = 4 × 7 ÷ 2 = 14
E[8d6]  = 8 × 7 ÷ 2 = 28

For 4d6 drop lowest, the expected value climbs to roughly 12.24 because you are throwing away the worst die each time. That is why this method produces ability scores that feel heroic compared to 3d6 straight.

Probability of a Single Die Result

A fair die is uniform, so each face comes up with probability 1 ÷ Y. For the common die types:

• d4: 1 ÷ 4 = 25% per face
• d6: 1 ÷ 6 ≈ 16.67% per face
• d8: 1 ÷ 8 = 12.5% per face
• d10: 1 ÷ 10 = 10% per face
• d12: 1 ÷ 12 ≈ 8.33% per face
• d20: 1 ÷ 20 = 5% per face (a natural 20 is 5%, so is a natural 1)
• d100: 1 ÷ 100 = 1% per face

Probability for Multi-Die Sums (2d6)

Once you roll more than one die, the distribution stops being flat. Sums near the middle are far more likely than extremes because many combinations produce them. For 2d6 there are 36 equally likely outcomes:

Sum   Ways   Probability
 2      1      1/36  ≈ 2.78%
 3      2      2/36  ≈ 5.56%
 4      3      3/36  ≈ 8.33%
 5      4      4/36  ≈ 11.11%
 6      5      5/36  ≈ 13.89%
 7      6      6/36  ≈ 16.67%   ← most likely
 8      5      5/36  ≈ 13.89%
 9      4      4/36  ≈ 11.11%
10      3      3/36  ≈ 8.33%
11      2      2/36  ≈ 5.56%
12      1      1/36  ≈ 2.78%

This is why 7 is the pivotal number in Catan and craps. Rolling snake eyes (2) or boxcars (12) is 36 times less likely than rolling a 7.

Advantage and Disadvantage (D&D 5e)

Advantage means roll 1d20 twice and take the higher result. Disadvantage means roll twice and take the lower. The underlying die is still uniform, but the resulting distribution is skewed:

Roll type         E[d20]    P(natural 20)
Normal 1d20       10.5       5%   (1/20)
Advantage         ≈ 13.83    9.75% (1 − 0.95²)
Disadvantage      ≈ 7.18     0.25% (0.05²)

Advantage shifts your expected roll by roughly +3.3, which is stronger than almost any flat +X modifier in the game. It nearly doubles your chance of a critical hit on a natural 20.

Quick Reference: Standard Die Types

A virtual dice roller is faster than reaching for a physical set, but it raises a reasonable question: is the randomness real? The short answer is that for tabletop use it is indistinguishable from a fair physical die, and in many ways it is more even. Here is what is actually going on under the hood, which systems lean on which dice, and why the plastic cubes in your dice bag are not as fair as you think.

Is an Online Dice Roller Truly Random?

This roll dice online tool calls your browser's built-in random number generator, which is a pseudo-random number generator (PRNG). A PRNG is deterministic under the hood: given the same seed, it produces the same sequence. Modern browser PRNGs are seeded from high-entropy operating-system sources and pass standard statistical tests for uniformity, so any bias is measured in parts per billion over billions of rolls. For tabletop D&D, board games, name generators, and classroom probability demos, the statistical deviation from a perfect uniform distribution is invisible. You would need to roll for years before a chi-squared test flagged anything. For gambling, legal lotteries, or cryptographic use, you should use a certified hardware RNG instead, because audit and regulation require provable randomness rather than "close enough."

RPG Systems and Their Signature Dice

Different game systems pick different dice because the shape of the die changes the feel of the game. A d20 is swingy and dramatic. A pool of d6s is predictable and tactical. Here is how the major systems divide up:

The d20 system remains the most recognizable because D&D 5e and Pathfinder 2e dominate published sales. Pool-based d6 and d10 systems feel smoother because averaging several dice compresses the distribution, as the 2d6 table in the previous section shows.

Common House Rules and Optional Mechanics

Home games almost always add a house rule or two on top of the printed dice rules. Some of the most common:

• Exploding dice. Whenever a die rolls its maximum (a 6 on a d6, say), roll it again and add. If the re-roll also maxes, keep going. Used in Savage Worlds, Shadowrun (rule of 6), and many indie games. Explosions raise expected value by roughly max ÷ (max − 1), so a d6 averages 4.2 instead of 3.5.
• Reroll 1s. The Great Weapon Fighting style in D&D 5e lets you reroll 1s and 2s on damage dice once. On a d6 damage die this pushes the average from 3.5 to about 4.17.
• Take 10 and Take 20. A legacy of D&D 3.5 and Pathfinder 1e. When you are not under pressure, you can skip the roll and count it as a 10 (average attempt) or spend 20 times as long to count it as a 20 (best possible effort).
• Drop-lowest ability scores. 4d6 drop lowest is the standard alternative to the 3d6 method for heroic characters.
• Heroic reroll or inspiration. Spend a meta-resource to reroll any single die. Most modern systems bake some version of this in.

Why Physical Dice Are Often Less Random

Physical dice are famously biased. A standard hobby-grade plastic d20 from a starter set typically has pip-drilled or injection-molded faces, rounded edges, and uneven plastic density. Testing by statisticians and dice manufacturers has documented biases of several percent per face. Casino-grade dice are a completely different product: machined to tolerances within 0.0005 inches, with flush painted pips so the weight distribution is even. They cost about 15 times more per die and are typically retired after eight hours of table play. A digital d20 roller does not wear, does not care which side you last set the die on, and does not have a pip-drilled face dragging the center of mass toward the 20.

For home play the bias in a good plastic set is harmless and is part of the charm. For tournament play, organized-play events, or probability experiments where fairness actually matters, a digital roller is the more neutral choice.