Random Number Generator
Random Number Generator
Pick a random number between any two numbers, or a whole list at once, with or without repeats, sorted or as drawn, and whole numbers or decimals. Every value in the range has exactly the same chance, and the odds are shown for each draw.
Where the numbers fell
Fairness check, 10,000 practice draws
Numbers come from the browser’s cryptographic random generator, the same source used for security keys. Each draw takes a 53 bit random integer and throws away the few values that would make some numbers more likely than others, so every value in the range has exactly the same chance. Decimals are drawn as whole numbers of hundredths or thousandths and divided back, so 0 to 1 with 2 places gives 101 equally likely values. Nothing is sent anywhere; the draw happens on your device. The CSV, image and printed report contain the numbers you drew and the settings you chose, nothing preloaded.
How to use this tool
Enter the lowest and highest numbers you want and press Generate. For more than one number, set How many; choose No repeats to draw each number at most once, and pick an order if you want the list sorted. Decimal places let you draw values such as 0.37 or 7.2.
The result appears at the top and in the list below it, with the chance of each number and the odds of guessing the whole draw. Earlier draws stay listed beside the result until you leave the page, and Copy numbers puts the list on your clipboard.
How the numbers are picked
Each draw starts from the browser's cryptographic generator, which supplies random bits that cannot be predicted. The tool takes 53 of them, a whole number from 0 to about 9 quadrillion, and turns it into a value in your range by taking the remainder after dividing by the number of possible values.
A plain remainder would be slightly unfair, because the random numbers rarely divide evenly into your range and the leftover block favours the smallest results. So any raw number that lands in that last incomplete block is thrown away and drawn again. The diagram shows the effect on a tiny source of 8 values; with 53 bits the thrown away share is too small to notice, but it keeps every result exactly equal.
Odds of guessing common draws
| Draw | Chance of each number | Odds of guessing the set, any order |
|---|---|---|
| 1 from 1 to 10 | 1 in 10 | 1 in 10 |
| 1 from 1 to 100 | 1 in 100 | 1 in 100 |
| 3 from 1 to 10 | 1 in 10 | 1 in 120 |
| 5 from 1 to 50 | 1 in 50 | 1 in 2,118,760 |
| 6 from 1 to 49 | 1 in 49 | 1 in 13,983,816 |
| 5 from 1 to 69 | 1 in 69 | 1 in 11,238,513 |
| 6 from 1 to 59 | 1 in 59 | 1 in 45,057,474 |
| 7 from 1 to 35 | 1 in 35 | 1 in 6,724,520 |
| 10 from 1 to 100 | 1 in 100 | 1 in 17,310,309,456,440 |
No repeats. With repeats allowed and the order mattering, the odds are the range size multiplied by itself once for each number.
A worked example you can check on paper
Drawing 6 numbers from 1 to 49 with no repeats, the first can be any of 49, the second any of the 48 left, and so on down to 44. That is 49 x 48 x 47 x 46 x 45 x 44, or 10,068,347,520 ordered draws.
The same six numbers can come out in 6 x 5 x 4 x 3 x 2 x 1, or 720, different orders, so the number of distinct sets is 10,068,347,520 divided by 720, which is 13,983,816. A single guess at the set therefore has a 1 in 13,983,816 chance.
Mistakes that catch people out
Thinking a number is due. A number that has not come up for a while is no more likely next time. Each draw is independent.
Expecting an even spread in a few draws. Ten draws from 1 to 10 will usually repeat something; the chance of no repeat at all is under 0.04 percent.
Avoiding patterns. The set 1, 2, 3, 4, 5, 6 is exactly as likely as any other six numbers; it only looks less random.
Rounding in spreadsheets. A formula that rounds a random fraction times 10 makes 0 and 10 half as likely as the numbers in between. Round down and add 1 instead, or use a function built for whole numbers.
Popular calculations
Each opens the generator with those settings and draws straight away. Press Generate for a new result, or change any setting once it is open.
One number from a range
Numbers with a set number of digits
Sets with no repeats
Random order
Dice and repeats
Decimals and negative numbers
How this was checked
The engine was tested in Node with the same cryptographic source a browser uses. In 200,000 draws from 1 to 100 the chi square statistic came out at 99.5 against 99 degrees of freedom, right where a fair generator should be, and 60,000 dice rolls landed within 2 percent of an even share on every face. No repeat draws were checked for duplicates, decimal draws for every possible value, and ranges up to a quadrillion for correct limits.
Every address in the lists above was then opened and checked for a distinct title, a result in range, charts that render, and clean CSV, image and print output containing only that draw, at desktop, tablet and phone widths.
Common questions
How do I pick a random number between 1 and 10?
Enter 1 in From and 10 in To, leave How many at 1 and press Generate. Each of the ten numbers has exactly a 1 in 10 chance on every press, whatever came up before.
Is this random number generator truly random?
It uses the browser's cryptographic generator, which is seeded from unpredictable hardware and system events and is the same source used to make security keys. The numbers cannot be predicted or reproduced, which makes them random for any draw, game or sample.
How do I get random numbers with no repeats?
Set Repeats to No repeats. Each number can then appear only once, like balls taken out of a drum, so you cannot ask for more numbers than the range holds: at most 10 from 1 to 10.
What are the odds of guessing 6 numbers from 1 to 49?
1 in 13,983,816 if the order does not matter. That is 49 x 48 x 47 x 46 x 45 x 44, the ways of drawing six in order, divided by 720, the ways of arranging six numbers.
Can it pick decimals or negative numbers?
Yes. Choose up to 4 decimal places, and enter any numbers for From and To, including negatives. Minus 10 to 10 has 21 whole numbers, each with a 1 in 21 chance.
Are some numbers luckier than others?
No. Every value has the same chance on every draw, and the generator has no memory. Runs, repeats and gaps look like patterns but turn up in random draws far more often than people expect.
Related Calculators and Reference
- Z Score Calculator: probabilities and percentiles on the normal curve.
- Standard Deviation Calculator: spread of a list of numbers.
- Scientific Calculator: powers, factorials and more with the working shown.
- Binary, Hex and Decimal Converter: see a number as the bits a computer holds.
- Permutation and Combination Calculator: count how many different draws are possible.
- Dice Probability Calculator: the exact odds of any dice roll.
- Chi Square Calculator: test a run of numbers for equal frequencies.
- MDN: Crypto.getRandomValues(): the browser random source used here.