Random number generator

Why the draw is fair

Your browser provides cryptographic random numbers (crypto.getRandomValues), far better than Math.random. But a plain remainder (x % n) favors small values whenever the range does not divide 2³² evenly. This generator throws away draws from the leftover zone instead:

\[ \begin{gathered} \text{limit} = \left\lfloor \dfrac{2^{32}}{n} \right\rfloor \times n \\ \text{if } x \geq \text{limit, draw again} \,;\ \text{otherwise result} = \text{min} + (x \bmod n) \end{gathered} \]

Over 1 million rolls between 1 and 6, each face comes up about 166,667 times, within a few hundred.

No repeats, decimals and common settings

With "No repeats" the tool shuffles the range with a partial Fisher-Yates shuffle, so every combination is equally likely, like drawing balls from a drum without putting them back.

In decimal mode, values are rounded to the number of places you choose.

When to use a random number

• Games and challenges: roll a die, decide who goes first.
• Classrooms and clubs: pick a student number or a raffle ticket.
• Testing: make sample values for a spreadsheet or a script.

For a legally regulated drawing, such as a public sweepstakes, follow your state's rules and use an independent witness. This tool does not replace an officially supervised drawing.