Picking a random number between 1 and 100 sounds like the simplest job in the world, yet it goes wrong in predictable ways: off-by-one errors, accidental repeats, and draws that nobody trusts. Whether you are running a raffle, choosing a student, or settling a friendly argument, a few rules keep the draw fair and believable.
Step 1: Fix the range, including both ends
Say the range out loud before you draw: from 1 to 100, including both 1 and 100. That word including matters, because many quick methods accidentally exclude one end. A common programming mistake multiplies a random decimal by 100 and rounds down, which gives 0 to 99, or by 101, which gives 0 to 100. The correct result must be able to return 1 and 100 with the same chance as every number in between. If you use a tool, check that it says both ends are included, and test it once with a small range, such as 1 to 2, to confirm both values can appear.
Step 2: Decide about repeats before you draw
If you need one number, repeats do not matter. If you need several, decide in advance whether repeats are allowed. Drawing with replacement means each draw is independent, so the same number can appear twice; drawing without replacement, also called unique mode, removes each drawn number from the pool. For prize winners, seats, or teams, unique mode is almost always what you want. For dice-style rolls or simulations, repeats are correct. Announce the rule before the first draw, because switching mid-draw looks like manipulation even when it is innocent.
Step 3: Understand why duplicates surprise people
People underestimate how often repeats happen. Draw ten numbers from 1 to 100 with repeats allowed, and the chance that at least two match is about 37 percent. Draw twenty, and it rises to about 87 percent. This is the same maths behind the birthday problem, and it catches many organisers off guard: a repeated number in a raffle draw is usually not cheating, just probability. If duplicates would cause an argument, use unique mode from the start and the problem disappears.
Step 4: Make the draw visible
A fair draw that nobody sees feels unfair. For a group, generate the number on a screen everyone can watch, or screen-record the draw for an online audience. If the draw is audited or involves money, use a tool that supports a seeded draw: publish the seed and the settings before the draw, so anyone can reproduce the same result afterwards and verify it. For casual draws, a single visible generation is enough. What destroys trust is not the method but the re-roll: never draw again because you dislike the result.
Other ranges and uses
The same method works for any range: 1 to 6 for a dice roll, 1 to 10 for a rating, 1 to 52 for a card, or 1 to 250 for raffle tickets. Set the minimum and maximum, choose how many numbers you need, set unique mode if repeats are unwanted, and generate. For classroom use, assign each student a number and draw to pick who answers, removing each picked student so everyone gets a turn. For games, a random number can set turn order, pick a starting player, or choose a scenario, all without argument, provided the rules were stated first.
Quick checklist
Confirm both ends are included, decide on repeats in advance, use unique mode for winners, generate once in view of the audience, and keep the result. Five small steps, and your random number will be random in fact and in appearance.
Try it free right here
Use the free Random Integer Generator — Pick Random Whole Numbers in Any Range below, right on this page. It runs in your browser and needs no sign-up. You can also open the full tool here: Random Integer Generator — Pick Random Whole Numbers in Any Range.