Are Online Dice Really Random? How Virtual Dice Work
By Matty Dice ·
If you have ever rolled three 1s in a row on a website, you have probably wondered whether the dice are rigged. It is a fair question. Here is how virtual dice actually work, what makes a good one, and how you can check any roller for yourself.
Where the numbers come from
Computers can't toss a cube across a table, so a dice roller asks a random number generator (RNG) for a number and turns it into a die face. There are two broad kinds of RNG:
- Pseudo-random generators, like JavaScript's
Math.random(), produce numbers from a formula. They look random and are fine for most games, but they are predictable if you know the starting point. - Cryptographically secure generators, like the browser's
crypto.getRandomValues(), are designed so that nobody can predict the next value, even after watching millions of previous ones. They mix in unpredictable data from the hardware and operating system.
The tools on Online Dice Free use the cryptographic generator for every roll, coin flip and spin.
The hidden trap: modulo bias
Getting a random number is only half the job. Turning it into a die face is where many rollers quietly go wrong. A common shortcut is to take a big random number and use the remainder after dividing by 6. Because the range of the big number usually isn't an exact multiple of 6, a few faces end up very slightly more likely than others.
The fix is simple: throw away the handful of values at the very top of the range that would cause the imbalance and draw again. It's called rejection sampling, and it is what our roller does, so each face of a d6, d20 or d100 has exactly the same chance.
Are real dice any fairer?
Usually not. Ordinary dice have drilled pips, which make the 6 side slightly lighter than the 1 side, and rounded corners that let them roll further on some faces. Tests on cheap d20s have found some faces coming up noticeably more often than others. Casino dice are precision-made with filled pips and sharp edges for exactly this reason.
Why streaks feel suspicious
Humans are bad at judging randomness. We expect results to alternate and spread out evenly, but real randomness is clumpy. Roll a die 100 times and you'll very likely see the same number three times in a row somewhere. Each roll is independent: the die doesn't "remember" that it just rolled a 1, so a 1 is exactly as likely next time as any other number.
Test a roller yourself
- Roll a single d6 at least 600 times (the dice roller history helps, or roll 10 dice at a time).
- Count how often each face appears. You'd expect about 100 each.
- Expect some spread: anything between roughly 80 and 120 per face is perfectly normal for 600 rolls.
- If one face is consistently far outside that range across several tests, be suspicious.
For quick, fair rolls on any device, try the dice roller, the D&D dice roller or a coin flip.