🎲 Random Number Generator 1 to 20

What is the Random Number Generator 1-20?

A 1 to 20 range fits a specific set of everyday tasks honestly. It matches a twenty sided die (d20), the polyhedral die used in tabletop role playing games to resolve actions with a wide spread of outcomes. It also suits picking one person from a class, team, or list of up to 20 entries, choosing a random question number from a bank of 20 flashcards or quiz items, or assigning turn order among up to 20 players. It is not a stand in for lotteries or games that use a different number of balls or squares, so this page sticks to what the range genuinely supports rather than stretching the claim.

Fairness works the same way here as in any well built generator. The tool reads raw entropy from your browser Web Crypto API, then uses rejection sampling to map that value into the 1 to 20 range without bias. A naive approach that takes a random value and reduces it with the remainder operator (modulo 20) would make the low numbers very slightly more likely than the high ones, because 20 rarely divides evenly into the source range. Rejection sampling discards the small uneven tail of values so every one of the 20 numbers, from 1 through 20 inclusive, has exactly the same chance of appearing.

The duplicates toggle controls whether repeats are allowed. Leave Allow duplicates ticked and each pick is independent, exactly like rolling a d20 more than once; the same face can come up twice in a row, which is normal, not a flaw. Untick it and the tool draws without replacement using a partial Fisher-Yates shuffle, so every number in your result is distinct. Because the 1 to 20 range only holds 20 values, unique mode can never return more than 20 numbers no matter how high you set the how many field.

The how many and sort controls round out the tool. How many decides the size of your draw, and sort simply reorders the results from lowest to highest for easier reading once they are generated. Neither setting changes which numbers are possible or how likely each one is; they only change how many you draw and how the output is displayed.

When to use it

• Rolling a virtual twenty sided die (d20) for tabletop role playing games such as Dungeons and Dragons.
• Picking one student, name, or item at random from a class list or roster of up to 20 entries.
• Assigning random turn order or player order among a group of up to 20 people.
• Choosing a random question number from a quiz bank or flashcard set of 20 questions.
• Running a quick guess the number warm up game with friends, family, or a classroom.
• Selecting a random level, scenario, or card number in a game that uses a 1 to 20 numbering scheme.

How to use the Random Number Generator 1-20

1. The minimum is already set to 1 and the maximum to 20, matching this exact range; leave them as is or edit them if you need a different span.
2. Set how many numbers you want to generate; it defaults to 1 for a single pick.
3. Tick Allow duplicates for independent picks like repeated d20 rolls, or untick it to draw unique numbers with no repeats.
4. Optionally tick Sort results to list multiple numbers in ascending order.
5. Click Generate for a fresh result, then click Copy to place the numbers on your clipboard.

Formula & method

Worked examples

Nearby ranges and what they genuinely suit

How the duplicates toggle changes a 1 to 20 draw

Common mistakes to avoid

• Asking for more than 20 unique numbers. With duplicates off, the tool cannot return more values than the range holds. Since 1 to 20 contains exactly 20 numbers, requesting 25 unique numbers is impossible; widen the range or allow duplicates instead.
• Assuming 20 is excluded from the range. The maximum is inclusive. A 1 to 20 range can genuinely return 20 itself, not just numbers up to 19, so all 20 whole numbers are reachable results.
• Expecting a single d20 roll to avoid repeats automatically. A single die roll should keep Allow duplicates ticked, since each roll is independent. Rolling a 14 twice in separate rolls is normal behaviour for a fair d20, not a bug in the tool.
• Trusting a simple modulo based script for a d20 roll. A basic script that takes a random value modulo 20 introduces a small bias toward the low end of the range. This tool avoids that with rejection sampling so every one of the 20 faces is equally likely.

Glossary

Random number generator (RNG)

A process that produces numbers that are hard to predict, with each allowed value equally likely within the chosen range.

Twenty sided die (d20)

A die with 20 faces numbered 1 to 20, used in tabletop role playing games to resolve actions across a wide spread of outcomes.

Uniform distribution

A spread where every value in the range has exactly the same probability of being chosen, so no number is favoured over another.

Cryptographically secure

Randomness drawn from a high quality system source that cannot be predicted or reproduced, as provided by the Web Crypto API.

With and without replacement

With replacement means each pick is independent and numbers can repeat. Without replacement means each value is used at most once, like dealing cards.

Modulo bias

A subtle skew that appears when a large random value is reduced with the remainder operator and the range does not divide evenly, making some numbers slightly more likely.

Frequently asked questions