Leave the seed empty for a fresh roll. Type a seed when you need the same faces again, for example to show a friend the roll you just got or to check a worked example on this page.
How to use
- Enter how many dice to roll, from 1 to 100, and how many sides each die has, from 2 to 1000.
- Enter a modifier if the rules add or subtract a number after the dice. Use 0 when they do not.
- Press Roll. Add a seed first if you want that exact roll to be repeatable.
Formula / how it works
The notation. NdS means N dice with S sides each. A d6 is the familiar cube, a d20 is the twenty-sided die used for many ability checks, and a d100 (or a pair of d10s, which this page does not simulate as percentile digits) is the large range. The roller accepts any whole number of sides from 2 to 1000, so a d4, a d8, a d12 and a coin-flip d2 are the same calculation with a different face count. Each face from 1 through S is equally likely.
What is added. The modifier is applied once, after the dice are summed. It is not added to each die. In 2d20+3, two faces are rolled, those faces are added, then 3 is added. A negative modifier is written with a minus sign and subtracted. The result separates “sum of dice” from “total” so you can see whether a high total came from the dice or from the modifier. A modifier of 0 is shown as +0 and does not change the sum.
The seed. With the seed box empty, each press draws new faces. With a seed filled in, the same count, sides, modifier and seed produce the same faces every time. The sequence comes from a small fixed generator (mulberry32) started from that seed, not from the computer’s clock. That is why the examples on this page can quote exact faces: seed 1842 on 2d20+3 is the faces 10 and 12. Change any one of those four inputs and the faces may change. The random number generator is the tool to use when you want a single number in a range and you do not care about dice notation.
Limits that keep the roll readable. More than 100 dice, or more than 1000 sides, is rejected. A hundred d20s is already a long list of faces. The modifier must be a whole number from -10000 to 10000. Fractions are rejected because dice faces and the usual modifiers are whole numbers. The roller does not drop the lowest die, does not explode on a maximum face, and does not roll with advantage. If your table uses one of those rules, roll the dice here and apply the rule yourself so the page is not quietly doing a different thing.
Fairness. Each face is chosen independently. Over a long series a fair d6 should show each face about one sixth of the time, but a short series will clump. Two sixes in a row is not a sign the seed is stuck; check that you did not reuse a seed. An empty seed never repeats on purpose.
Showing your work. The first line repeats the notation, including the modifier when it is not zero. Then the faces, the sum, the modifier and the total. Copy that block if a game asks you to record the roll. A seeded roll also prints the seed so someone else can press Roll and see the same faces.
Worked examples
A seeded 2d20+3
Inputs: Number of dice: 2 | Sides: 20 | Modifier: 3 | Seed: 1842
Enter 2 dice, 20 sides, modifier 3 and seed 1842, then press Roll. The faces are fixed by that seed, so the total is the same on every visit.
Result: Dice: 2d20+3
Rolls: 10, 12
Sum of dice: 22
Modifier: +3
Total: 25
Seed: 1842
Sum 22 plus the modifier 3 is the total 25.
One familiar cube
Inputs: Number of dice: 1 | Sides: 6 | Modifier: 0 | Seed: 99
Enter 1 die, 6 sides, modifier 0 and seed 99. This is a single d6 with nothing added after the face.
Result: Dice: 1d6
Rolls: 2
Sum of dice: 2
Modifier: +0
Total: 2
Seed: 99
Seed 99 lands on the face 2.
Use cases
- Tabletop attacks and checks written as NdS+modifier.
- A repeatable roll when you need to show the faces to someone else.
- Board-game movement on a d6 without hunting for a physical die.
- Classroom probability, where a seed makes a demonstration replayable.
Tips & limitations
- Put the modifier in its own box. It is added once, not once per die.
- Clear the seed when you want a new roll.
- Keep the seed when you want to prove which faces came up.
- Apply advantage, drop-lowest or exploding sixes yourself; this roller does not.
FAQ
Does 2d20+3 add 3 to each die?
No. The two faces are summed, then 3 is added once. The line “Sum of dice” is the faces alone.
Why does the same seed always give the same faces?
The seed starts a fixed sequence. Same dice, same sides, same modifier, same seed: same faces.
What happens if I leave the seed empty?
Each press draws new faces. Nothing is stored between visits.
Can I roll a coin or a d100?
A coin is 1 die with 2 sides. A d100 is 1 die with 100 sides. Percentile dice that read tens and ones separately are not modeled.
Why is there a cap of 100 dice?
So the list of faces stays something you can read and copy. Roll again if a game truly needs more.
Are the rolls uploaded?
No. Faces are chosen in your browser.
Results are calculated from the values you enter. Double-check measurements and allow a margin before buying materials or making decisions.