Dice Roller

DICE FUN RANDOM RPG TABLETOP
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By Checked against sources by , Founder & Architect, RECATOOLS Published Updated Last reviewed

Dice roller. Roll D4, D6, D8, D10, D12, D20, D100 and custom dice. Advantage/disadvantage, modifiers, roll history. Free, no signup.

RT-FUN-005 · Fun & Misc
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Dice Roller Tool

Click a dice button above to add dice to your roll.

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How to Use the Dice Roller

Select your dice type

Click the dice type buttons — D4, D6, D8, D10, D12, D20, or D100 — to add dice to your roll. Each click adds one die of that type to the active pool. You can mix and match any combination.

Adjust quantities and add custom dice

Adjust quantities with the + and − buttons next to each die in your pool. Add a custom die by entering any number of sides in the Custom Die field — ideal for unusual polyhedral dice or house-ruled games.

Set modifier and advantage

Add a modifier (positive or negative) to be added to your total — used in D&D 5e for ability and proficiency bonuses. When you have a single die in the pool, toggle Advantage or Disadvantage for D&D-style rolls that keep the higher or lower of two results.

Roll and review results

Hit the big Roll button — individual results appear with animation, plus a running total. Every roll is saved to the collapsible Roll History table so you can track your session without taking notes.

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Dice, Probability and the Mathematics of Tabletop Games

The Mathematics of Dice: Probability Distributions Explained Simply

Every die is a random variable with a uniform distribution — each face has an equal probability of appearing. A standard six-sided die (D6) has a mean (expected value) of 3.5, calculated as (1+2+3+4+5+6) ÷ 6. This simple number has profound implications when you start combining dice.

Roll a single D12 and every result from 1 to 12 is equally likely — a flat, uniform distribution. Roll two D6 dice and the distribution changes completely. Seven becomes the most likely result because it can be made in six different ways: 1+6, 2+5, 3+4, 4+3, 5+2, and 6+1. Snake eyes (2) and boxcars (12) can only be made one way each. The result is a bell curve — mathematically, a discrete approximation of the normal distribution. This is the central limit theorem in action: as you sum more independent random variables, the distribution converges toward a bell curve, regardless of the shape of the original distribution.

"Rolling two D6 dice produces a bell curve with 7 as the most common result — appearing 1 in 6 times. Roll one D12 and every number is equally likely."

For tabletop RPG players, this statistical distinction is critical. The D12 greataxe and the 2×D6 greatsword in D&D 5e have nearly identical average damage (6.5 vs. 7), but their variance profiles are completely different. The greataxe gives you a higher chance of extreme results — a 1 or a 12 — while the greatsword clusters results near 7, making it more reliable but less swingy. Understanding this helps players make informed character-building decisions.

The mathematics of advantage and disadvantage (rolling two dice and keeping the higher or lower) also deserves attention. In D&D 5e, a natural 20 critical hit has a 5% probability on a single D20 roll. With Advantage — rolling two D20s and keeping the higher — the critical hit probability rises to approximately 9.75%. This is calculated as: 1 - (19/20)² = 1 - 0.9025 = 0.0975, or about one-in-ten. Across a long adventuring career, that nearly-doubled crit rate from Advantage makes a measurable difference to a character's output.

Tabletop RPGs in Singapore and Southeast Asia

The tabletop gaming revival of the 2010s reached Southeast Asia too. In Singapore, games that were once bought and played mostly around specialist hobby shops now also run in board-game cafés, at organised events and in groups that meet online.

Dungeons & Dragons 5th Edition, released by Wizards of the Coast in 2014, drove much of this growth. The streamlined ruleset lowered the barrier to entry compared to earlier editions, attracting a new generation of players who had encountered the game through streaming shows like Critical Role. The cultural mainstream moment arrived with the 2023 film Dungeons & Dragons: Honor Among Thieves, which introduced the hobby to audiences who might never have rolled a die before.

Across the region, from Kuala Lumpur to Manila, many tabletop role-playing groups play at least partly online. Virtual tabletops, Discord servers and digital character sheets mean a group no longer needs everyone in the same room, which matters in a region spread across islands and several time zones. A browser dice roller fills the same gap: everyone can see the same roll without a physical die on the table.

Why True Randomness Matters — and How Computers Achieve It

Physical dice are not perfectly fair. Drilled pips remove different amounts of material from different faces, and injection-moulded dice can carry air bubbles, uneven edges or rounded corners, so a cheap die can lean towards some faces more than others. How large that bias is depends on the individual die, which is why a die that "feels lucky" is hard to prove or disprove at the table.

Software dice rollers face a different challenge: most programming environments use pseudorandom number generators (PRNGs) that produce sequences that look random but are entirely deterministic. Given the same seed, a PRNG produces the same sequence every time. For casual use this is fine, but for applications requiring cryptographic quality randomness — gambling platforms, online casinos, randomised security tokens — PRNGs are unsuitable. The JavaScript Math.random() function is a PRNG and should never be used for security-sensitive applications.

This dice roller uses crypto.getRandomValues(), a Web Cryptography API that sources entropy from the operating system's hardware random number generator. Modern CPUs contain dedicated hardware entropy sources — Intel's RDRAND instruction gathers entropy from thermal noise in transistors; ARM processors use similar mechanisms. This hardware entropy is then conditioned through a CSPRNG (cryptographically secure pseudorandom number generator) to produce a high-quality, unbiased random stream. NIST Special Publication 800-90A (Barker and Kelsey, 2015) specifies deterministic random bit generators of this kind, built on hash functions or block ciphers. The crypto.getRandomValues() call used here draws on that operating-system source, so each roll behaves like a perfectly balanced die, without the pip bias.

The probability underneath the table

01

The most common result when rolling two D6 dice is 7 — it can be made in 6 ways (1+6, 2+5, 3+4, 4+3, 5+2, 6+1), giving a 1-in-6 probability.

02

A D20 natural 20 (critical hit in D&D 5e) has a 5% probability — with Advantage (roll twice, take higher), the critical hit chance rises to approximately 9.75%.

03

Dungeons & Dragons was first published by Gary Gygax and Dave Arneson in 1974. For its 50th anniversary in 2024, Hasbro's Wizards of the Coast put its audience at more than 50 million fans.

04

Rolling 3D6, a total of 10 or 11 each comes up 27 times in 216 (12.5%), while 3 or 18 comes up only once in 216 (about 0.46%).

05

The D100 (percentile die) in tabletop RPGs is typically rolled as two D10s — one for the tens digit (0–90) and one for the ones digit (0–9), giving results from 1–100.

06

The "4D6 drop lowest" method for ability scores averages about 12.24 per score, against 10.5 for a straight 3D6 roll.

07

With Disadvantage (roll twice, take lower), a natural 20 drops to 0.25% (1 in 400), and a natural 1 rises to 9.75%.

08

A D12 greataxe averages 6.5 damage and a 2×D6 greatsword averages 7. The averages are close, but 2×D6 clusters around 7 while every D12 result from 1 to 12 is equally likely.

09

An attack that needs 11 or higher on a D20 hits 50% of the time. With Advantage the same attack hits 75% of the time, because it misses only when both dice show 10 or lower.

10

The average of a D20 rolled with Advantage is 13.825, and with Disadvantage 7.175, against 10.5 for a single roll.

📅 Research current as of 01 Oct 2026 · Sources: W3C. Web Cryptography API, W3C Recommendation 26 January 2017 — getRandomValues: https://www.w3.org/TR/2017/REC-WebCryptoAPI-20170126/; Wizards of the Coast. System Reference Document 5.1 (Creative Commons Attribution 4.0) — Advantage and Disadvantage; Ability Scores and Modifiers: https://www.d
Standards, published formulas, and reference data are revised over time — check against a current authoritative source before relying on these figures.

Frequently Asked Questions

  • The "D" stands for die (or dice), and the number is the number of sides. A D6 is a standard six-sided die — the kind used in Monopoly or Yahtzee. A D20 is a twenty-sided die used in Dungeons & Dragons for attack rolls, saving throws, and ability checks. A D100 (also called a percentile die) produces results from 1 to 100 and is used for percentage-based tables in many RPG systems. Common polyhedral dice used in tabletop RPGs are D4, D6, D8, D10, D12, D20, and D100.
  • Advantage means you roll two D20 dice and keep the higher result. Disadvantage means you roll two D20 dice and keep the lower result. Advantage is granted for favourable conditions — attacking an unseen enemy, having a helpful ally, or using certain spells. Disadvantage applies in unfavourable conditions. A roll cannot have both simultaneously. This mechanic replaces the older system of numerical bonuses and penalties, making the maths simpler. With Advantage, your effective average roll rises from 10.5 to about 13.8 on a D20.
  • A modifier is a fixed number added to (or subtracted from) the result of a dice roll. In D&D 5e, ability score modifiers range from −5 to +10. For example, a character with Strength 18 has a +4 modifier — when they roll a D20 to attack, they add +4 to whatever the die shows. Enter a positive number (e.g. 3) for a bonus or a negative number (e.g. −2) for a penalty. The modifier is applied once per roll expression, regardless of how many dice are in the pool.
  • On a single D20, the probability of rolling a 20 is exactly 1 in 20, or 5%. With Advantage (rolling two D20s and keeping the higher), the probability rises to approximately 9.75% — calculated as 1 − (19/20)² = 0.0975. With Disadvantage the probability drops to about 0.25% — calculated as (1/20)² = 0.0025. In D&D 5e, a natural 20 on an attack roll is an automatic critical hit, dealing double damage dice regardless of the target's armour class.
  • They have nearly the same average (2D6 = 7, D12 = 6.5) but very different probability distributions. A D12 has a uniform distribution — every result from 1 to 12 has an equal 1-in-12 chance. Two D6 dice produce a bell curve: results near 7 are far more likely than extreme results like 2 or 12. This makes 2D6 more consistent and predictable, while the D12 is more "swingy." In D&D weapon terms, a greatsword (2D6) deals reliably middling damage, while a greataxe (D12) has a higher chance of both very low and very high rolls.
  • Yes — RECATOOLS Dice Roller uses crypto.getRandomValues(), the Web Cryptography API, which sources entropy from your device's hardware random number generator. This is a cryptographically secure source of randomness — the same mechanism used by password managers and encrypted communications. It is statistically superior to JavaScript's Math.random(), which is a deterministic pseudorandom number generator and should not be used for fair dice simulation. Our implementation also uses rejection sampling to eliminate modulo bias, ensuring every face has an exactly equal probability.
  • The standard D&D 5e method is "4d6 drop lowest" — roll four D6 dice and discard the lowest result, keeping the sum of the top three. Repeat six times for six ability scores. To use this roller, set your pool to 4×D6 and set Number of Rolls to 6. Roll and note the top three dice from each roll (ignore the lowest individual die). The Roll History table records all six rolls so you can compare. Alternatively, use the standard array (15, 14, 13, 12, 10, 8) for a more balanced character.
  • A D100 or percentile roll produces a result from 1 to 100, representing a percentage chance. It is used in many RPGs for random tables — "roll percentile; on 01–25 the encounter is friendly, on 26–75 it is neutral, on 76–100 it is hostile." Physically, it is usually rolled as two D10 dice — one representing tens (00, 10, 20… 90) and one representing units (0–9). A result of 00 on the tens die and 0 on the units die equals 100. This roller simulates D100 directly using hardware-random integers in the range 1–100.
  • Mathematically, a fair die can have any number of sides, as long as each face has equal area. In practice, the Platonic solids — tetrahedron (D4), cube (D6), octahedron (D8), dodecahedron (D12), and icosahedron (D20) — are perfectly fair. The D10 and D100 are not Platonic solids but are still widely used. Unusual commercial dice exist in D3, D5, D7, D14, D16, D24, D30, and even D100 physical form. This roller's Custom Die field accepts any value from 2 to 99,999 sides, so you can simulate any polyhedral die imaginable.
  • Yes, the odds are identical. With two fair D10s, one for the tens and one for the units, each of the 100 combinations is equally likely, so every result from 1 to 100 has a 1-in-100 chance. This roller skips the two-dice step and picks a whole number from 1 to 100 directly, throwing away any random value that would make some results slightly more likely than others. Either way, 37 is exactly as likely as 100. Every roll is worked out in your browser and nothing is sent to a server.

Method & sources

How it computes

Each die is an independent uniform draw: a 32-bit value from crypto.getRandomValues is rejection-sampled (values at or above the largest multiple of the face count are discarded) and reduced modulo the face count, so every face has exactly equal probability. Totals sum the kept dice; a modifier is added once per roll; Advantage/Disadvantage rolls a single die twice and keeps the higher/lower result.

What this tool implements

  • Randomness from the W3C Web Cryptography API getRandomValues (the operating system's CSPRNG), never Math.random; modulo bias is removed by rejection sampling.
  • Advantage/Disadvantage and modifiers follow the D&D 5th-edition System Reference Document (SRD 5.1, CC BY 4.0): roll two d20 and keep the higher (advantage) or lower (disadvantage); a modifier is a fixed bonus added to the total.
  • Stated probabilities are exact combinatorics: P(natural 20) = 1/20 = 5%; with advantage 1 − (19/20)² = 9.75%; with disadvantage (1/20)² = 0.25%; mean d20 with advantage = 13.825; 2d6 sums peak at 7 (6 of 36).
  • D100 is drawn directly as a uniform integer 1–100, not as two d10.

Sources

What can make this go out of date

  • none at runtime
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