Random Number Generator
Use this random number generator to pick a number between any two numbers in one tap. Pick a random number from 1 to 100, 1 to 10 or a range of your own, or generate random numbers, up to 100 at once, with no repeats. Open More options for decimals, even or odd numbers, multiples and numbers to leave out, and show any result as words, Roman numerals, binary or hex. Every number is drawn securely in your browser, so it is a fair random number picker for classrooms, games, giveaways and quick decisions.
Part of Randomfella’s free random tools. See every tool and guide on the home page.
How a random number generator works
Picking a Random Number Between Two Numbers
A fair random number generator gives every allowed number the same chance. Pick a number between 1 and 100 and each number comes up 1 time in 100; pick between 1 and 10 and each comes up 1 time in 10. Every draw is independent, so earlier numbers never change what comes next.
Why the Same Number Can Come Up Twice
Repeats are normal. If you generate 10 numbers from 1 to 100 and repeats are allowed, there is about a 37% chance that at least two match. With 13 numbers it is better than even, about 56%. This is the same effect as the birthday problem.
Random Numbers With No Repeats
Switch on No repeats and each number can appear only once in a draw, like pulling numbered tickets from a bag without putting them back. Ten different numbers from 1 to 100 can be chosen in 17,310,309,456,440 ways, and every one of those sets is equally likely.
How Unique Numbers Are Drawn
Randomfella uses a partial shuffle: it picks one number, then picks the next from what is left, and so on. It does this without building a list of every number, so asking for 10 different numbers from a range of a billion is as quick as asking for 10 from 100.
Decimals, Even Numbers and Multiples
The settings under More options change which numbers are allowed, not how fairly they are picked. The tool works out the full set of allowed numbers first and then picks one position in that set at random, so every allowed number is exactly as likely as every other:
- Decimals: with 2 decimal places, 0 to 1 has 101 equally likely values, from 0.00 to 1.00
- Even or odd only: 1 to 100 has 50 even numbers, so each comes up 1 time in 50
- Multiples of 5: 1 to 100 gives 5, 10, 15 and so on up to 100, 20 values in all
- Leave out numbers: each number you exclude simply leaves the set, and the rest share the chance equally
Streaks and Repeats Are Normal
Random sequences contain runs and repeats. After the same number comes up twice, the next draw is still a fresh draw with the same odds. A number is never “due”, and a number that has not appeared for a while is no more likely to appear next.
Technical Specs: How Randomfella Picks a Number
Randomfella uses your browser’s built-in cryptographic random number generator, window.crypto.getRandomValues(), for every number. It never uses Math.random().
No Modulo Bias
A naive method that takes a random number modulo the size of the range slightly favours some numbers. Randomfella uses rejection sampling instead: a value that would cause bias is thrown away and drawn again. For a range of 100 numbers only 96 of the 4,294,967,296 possible raw values are ever rejected, so every number has exactly the same probability.
Result First, Then Animation
The numbers are decided before the reels start to spin. The animation only shows the result that has already been chosen, and nothing is sent to a server.
Random Number Generator FAQ
Fairness and privacy
Is this random number generator really fair?
Yes. Every number uses your browser’s secure random number generator (Web Crypto API), with a method that removes modulo bias, so each allowed number is exactly as likely as every other. The numbers are decided before the animation starts, so the animation can’t influence them.
Does it store or send my numbers anywhere?
Your settings, history and awards stay on your device. The page uses anonymous analytics that count how often Generate is pressed and how many numbers were asked for, but never the numbers themselves.
Why did I get the same number twice?
Repeats happen naturally. Ten numbers from 1 to 100 contain a repeat about 37% of the time when repeats are allowed. Switch on No repeats if you want every number in a draw to be different.
Using the tool
How do I pick a number between 1 and 100?
Press Generate. The tool starts at 1 to 100. To change the range, type a new minimum and maximum, or tap a preset such as 1 to 10.
How do I generate several random numbers at once?
Set How many numbers to anything from 1 to 100, or tap 5, 10 or 100. With No repeats on, every number in the draw is different, which suits picking a set of different numbers from a range.
What is the biggest range I can use?
Whole numbers can go from −1,000,000,000 to 1,000,000,000. With decimals the range is a little narrower, because the number of possible values is capped at about 4.29 billion.
Can I generate random decimals?
Yes. Under More options, set Decimal places from 1 to 4 and every value in the range, such as 3.47, is equally likely.
Can I leave out some numbers, or pick only even numbers?
Yes. Under More options you can list numbers to leave out, choose even or odd only, or pick only multiples of a number such as 5 or 10.
What does Show as do?
It writes the result as digits, words (in English, Spanish, French or Arabic), Roman numerals, binary or hex. Roman numerals work for 1 to 3999, and binary and hex for whole numbers.
Extra features
What is Call it?
Type a guess before you press Generate. If the single number that comes up matches, you called it. The odds are shown in the Awards tab.
Can I download my results?
Yes. You can export your history to CSV with timestamps, the range and every number. The file records what happened on your device.
Can I put the random number generator on my own website?
Yes. There is a free embeddable widget and a small script for developers, with no account or key. See the embed page for the code.
Does it work in other languages?
Yes — English, Spanish, French and Arabic.
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