Random Number Generator

How the numbers are chosen

Each draw comes from your browser’s cryptographic random number generator (crypto.getRandomValues), the same source used to create passwords and encryption keys. It produces 32 random bits at a time, and the calculator turns them into a number in your range by rejection sampling: if the bits fall in the small leftover part that would make some numbers slightly more likely, they are thrown away and new ones are drawn. A common shortcut — taking the remainder after dividing by the range size — would favor low numbers by a tiny amount; this method keeps every value exactly as likely as every other.

The numbers are made on your device when you press Generate. Nothing is sent to a server, and the share link saves only the settings — range, count, repeats, order and decimal places — so a friend who opens it makes their own draw.

Repeats or no repeats

With No repeats on, the generator works like drawing tickets from a hat without putting them back: 10 numbers from 1 to 10 is a shuffle of all ten. Use it for raffles, picking students, assigning order or sampling without duplicates. With repeats allowed, each draw is independent, like rolling a die again and again — the right choice for games and simulations. For dice with a running total, use the dice roller; for heads or tails, the coin flipper.

The odds

Matches come up more often than intuition suggests. Draw 10 numbers from 1 to 100 with repeats allowed and there is a 37% chance that at least two are the same — the same effect that makes a shared birthday likely in a group of only 23 people. When the result lists several numbers, the calculator also shows the chance of drawing that exact set. To work out other combinations by hand — 49 × 48 × 47 × 46 × 45 × 44 divided by 6! — the scientific calculator has the factorial key. For percentages and probabilities from your own counts, the percentage calculator does the division.

Random decimals and negative numbers

Set the decimal places to draw values such as 0.37 or 12.5: with 2 places, the range 0 to 1 holds 101 equally likely values, from 0.00 to 1.00. Negative limits work the same way — −10 to 10 includes zero and 21 whole numbers. Sorting from low to high helps when you draw many numbers, and the full list can be copied or downloaded as a CSV file for a spreadsheet. To write a random decimal such as 0.375 as a fraction, use the decimal to fraction calculator.

When not to use it

A web page is fine for games, classrooms, giveaways among friends and everyday choices. Official lotteries and regulated drawings use certified equipment and witnessed procedures, and security keys should come from your operating system or a password manager rather than from a number you copy off a screen. To pick numbers in the format of a specific lottery, see the lottery number generator.