How to use the random number picker
The generator opens set to one whole number from 1 to 100. Change the limits, the count and the options, then press Generate numbers. With no seed, every press gives a fresh batch.
Pick Unique values only when you can't have the same number twice, like drawing raffle tickets or assigning seats. Leave repeats on when each pick should be independent, like rolling a die over and over.
- Enter the lower and upper limits. Both are included.
- Choose how many numbers you want, from 1 to 200.
- Pick Integer or Decimal, and set decimal places if needed.
- Choose Allow repeats or Unique values only.
- Pick generated, ascending or descending order, then press Generate numbers.
Random number generator 1-10 and 1-100
Both limits count, so a range from a to b holds b - a + 1 numbers. 1 to 10 has 10 possible results and 1 to 100 has 100. Each one is equally likely on every draw, and over many draws the average settles near the middle of the range.
Repeats come up sooner than most people expect when repeats are allowed. Draw just 5 numbers from 1 to 10 and there's a 69.76% chance at least two match. Choose Unique values only if that would be a problem.
Possible values = upper limit - lower limit + 1Chance of any one value = 1 / possible valuesChance of at least one repeat in k draws = 1 - (n x (n - 1) x ... x (n - k + 1)) / n^k
| Range | Possible numbers | Chance of any one number | Long-run average | Chance of a repeat in 5 draws (repeats allowed) |
|---|---|---|---|---|
| 1 to 6 | 6 | 16.67% | 3.5 | 90.74% |
| 1 to 10 | 10 | 10% | 5.5 | 69.76% |
| 1 to 20 | 20 | 5% | 10.5 | 41.86% |
| 1 to 50 | 50 | 2% | 25.5 | 18.64% |
| 1 to 100 | 100 | 1% | 50.5 | 9.65% |
Random numbers without repeats
Unique values only samples without replacement: once a number is picked, it's out for the rest of that batch. You can't ask for more unique numbers than the range holds. Six unique numbers from 1 to 6 always returns all six in some order, and a request for seven is rejected.
Large ranges work too. Integer limits can be up to 200 digits long, and the tool picks unique values without building a list of every number in the range.
Decimal mode and fixed decimal places
Decimal mode splits the range into equal steps at the number of places you choose, from 0 to 50. At two places, 0.20 to 0.25 has six possible values: 0.20, 0.21, 0.22, 0.23, 0.24 and 0.25. Each is equally likely.
If a limit has more decimal places than you selected, the tool rejects it instead of quietly rounding. In Integer mode, fractional limits shrink to the whole numbers inside them, so 0.2 to 112.5 becomes 1 to 112.
How the numbers are generated
With the seed left blank, the tool asks your browser for random bytes through crypto.getRandomValues(), part of the Web Crypto API. Browsers produce these with a cryptographically secure pseudo-random generator seeded from the operating system's entropy. It doesn't use Math.random(), which MDN says isn't suitable for anything security related.
To fit those bytes to your range, the tool keeps only as many bits as the range needs and throws away any value that lands past the top, then draws again. For 1 to 10, it reads 4 bits (16 possible values), keeps the 10 that map to your range and redraws the other 6. That rejection step is what keeps every number equally likely.
What the seed does
Typing a seed switches to a small deterministic generator. The same seed with the same settings gives the same batch every time, which helps for lessons, demos and software tests where someone needs to check your results.
Seeded output is predictable by design, so it's not secure. Never use it for passwords, keys, tokens, prize draws or anything where someone could gain by guessing the next number.
When to use something else
This picker is fine for classroom questions, turn order, games, sample data and casual giveaways among friends. For lotteries, regulated gambling, paid prize draws, legal selection or research randomization, use an audited process that meets the rules you're under, with records and witnesses as required. Nothing here is stored or logged for later proof.
Sources
These references cover the browser random source and the standards for secure random generation.