Random Number Generator

How to use the random number generator

1. Enter the Minimum and Maximum. Both limits are included, so 1 and 6 behaves like a die. If you type them the wrong way round, the tool swaps them.
2. Set How many numbers you want, from 1 to 10,000.
3. Under Number type, keep Integers or choose Decimals and set the Decimal places (1 to 10).
4. Tick No duplicates (unique numbers) if each value may appear only once, as in a lottery or a raffle.
5. Pick an Order (Random order, Smallest first or Largest first) and a Separator (New line, Comma or Space).
6. Press Generate. Copy the list or download it as a text file. A single result is also shown in large type, which is handy for classrooms and live draws.

Below the list, Possible values tells you how many different numbers the range contains, and Sum adds up the drawn numbers.

How the numbers are drawn

The numbers come from the Web Crypto API built into your browser (crypto.getRandomValues), the same source used for encryption keys, not from Math.random(). Converting random bits into a range can introduce a subtle bias: if you reduce a 32-bit number modulo 6, some results come up very slightly more often than others. This tool avoids that with rejection sampling: random values that would favour some results are thrown away and redrawn, so every number in the range has exactly the same probability.

Decimals are handled the same way. With 2 decimal places, the range 0 to 1 contains 101 possible values (0.00, 0.01 … 1.00), and each one is equally likely. The tool works internally with whole units of 0.01, so you never get rounding artefacts such as 0.30000000000000004, and the minimum and maximum can both come up.

For No duplicates, the tool uses Floyd’s sampling algorithm, which picks distinct values without listing the whole range first. That is why you can draw 100 unique numbers between 0 and one quadrillion instantly. The only limit is logical: you cannot draw more unique numbers than the range contains. Asking for 7 unique numbers between 1 and 6 shows an error instead of looping forever.

Everything runs locally. The numbers are generated on your device and are not sent anywhere or stored.

Examples

• Dice roll: minimum 1, maximum 6, one number. For two dice, ask for two numbers with duplicates allowed.
• Lottery-style pick: minimum 1, maximum 49, six numbers, No duplicates, Smallest first.
• Raffle tickets: if the tickets go from 1001 to 1250, enter those limits and the number of prizes, with No duplicates ticked.
• Random sample of rows: to audit 20 rows of a 5,000-row spreadsheet, draw 20 unique numbers between 2 and 5001, then use Comma to paste them into a filter.
• Test data: 1,000 decimals between -50 and 50 with 3 places, one per line, ready to paste into a spreadsheet column.