Random number between 1 and 20

Pick a number between 1 and 20

The generator is set from 1 to 20, the range of a twenty-sided die or a class of twenty pupils. Click “Pick a number” or press the space bar: the number comes from your browser's cryptographic random generator, and all twenty values have the same chance. No data is sent anywhere.

At the table or in the classroom

Tabletop role-playing games

In most tabletop RPGs, the twenty-sided die settles attacks and skill checks. No d20 to hand? This page does the job. For a roll with advantage (two dice, keep the higher), set “How many numbers” to 2.

At school

• Cold-calling a pupil: number the class register and draw. With 24 pupils, raise the maximum to 24.
• Picking a question from 20 prepared for an oral or a revision session. For a five-question quiz, ask for 5 numbers with “No duplicates”.
• Choosing an exercise or a page in a chapter that has twenty.

Your odds from 1 to 20

• One specific number, such as a natural 20 for a critical hit: 1 in 20, or 5%. A critical fail on a 1: also 5%.
• Rolling 15 or more: 6 values out of 20 (15 to 20), or 30%.
• At least one 20 on a roll with advantage: 1 − (19/20)² = 39/400, or 9.75%.
• For one pupil, being picked in a single draw: 5%. Never being picked in five separate draws: (19/20) to the power of 5, or 77.38%.

That last figure explains the feeling that “it's always the same people”: over a week of five draws, most pupils are never picked, and now and then the same pupil is picked twice.

FAQ

How do I make sure every pupil goes exactly once?

Ask for 20 numbers and tick “No duplicates”: you get a full running order where each number appears once.

Is this fairer than a real d20?

Here all twenty results have exactly the same probability. A moulded die can have small flaws that favour some faces.