Calculator · Windows 10 and 11
Dice roller
Choose how many dice and how many sides, add a number to the total if the game asks for one, and roll. The dice tumble and land, the total shows beside the button with how it was added up, and every roll is kept in a list. For board games, tabletop role-playing games and classroom probability.
How to roll dice in Octoolo
- 1
Open Roll dice
In Octoolo's Calculator, pick Roll dice in the Chance group. It opens with two six-sided dice already rolled.
- 2
Choose the dice
Type the number of Dice (1 to 100) and pick the Sides: d4, d6, d8, d10, d12, d20 or d100.
- 3
Add a modifier
Type a number in Add to the total, such as 3 or −1. The button then reads like Roll 2d6 + 3.
- 4
Roll
Press the Roll button or click the dice. The total appears beside the button with each die added up; Copy copies it. Below, Rolls, newest first lists every roll; Copy takes the list and Clear empties it.
Dice notation: what 3d6 + 2 means
Games write dice as numberdsides: 3d6 means three six-sided dice added together, d20 one twenty-sided die, and 2d6 + 2 two six-sided dice plus 2. Octoolo writes its button the same way, so Roll 3d6 + 2 rolls three dice and adds 2.
Below the dice, the tiles give the Lowest possible and Highest possible totals and the Average, which is the number of dice × (sides + 1) ÷ 2, plus the modifier. For 3d6 + 2 that is 5 to 20 with an average of 12.5. The modifier can be negative: 1d20 − 1 runs from 0 to 19.
d100, often called percentile dice, is one die from 1 to 100 here. Tables that use two d10s (tens and units) read 00 and 0 as 100, which gives the same 1 to 100 range.
The odds of each total
One die gives every face the same chance: 1 in 6 on a d6, 5% on a d20. Adding dice changes that, because middle totals can be made in more ways:
| Total of 2d6 | Ways | Chance |
|---|---|---|
| 2 or 12 | 1 | 2.8% |
| 3 or 11 | 2 | 5.6% |
| 4 or 10 | 3 | 8.3% |
| 5 or 9 | 4 | 11.1% |
| 6 or 8 | 5 | 13.9% |
| 7 | 6 | 16.7% |
That is why 7 is the robber in board games built on two dice, and why 3d6 gives scores that cluster near 10 and 11 while 1d20 spreads them evenly. With advantage in tabletop role-playing games (roll two d20 and keep the higher), the chance of at least one 20 rises from 5% to 9.75%; roll 2d20 here and take the higher die from the list.
How the dice are rolled
Each die is a whole number drawn from your computer's cryptographic random source. Turning a random number into 1 to 6 with a plain remainder would make some faces slightly likelier than others, so the roller throws away the few values that would cause that and draws again: every face is exactly as likely. The tumbling you see is decoration; the roll is decided before the dice move.
Changing the number of dice or the sides shows a fresh roll of the new set at once, so what you see always matches the button. With many dice the faces get smaller: up to 12 dice at full size, then smaller ones, and up to 100 in all. If Windows is set to show less animation, the dice land without tumbling.
For a single number in a range other than a die's, use the random number generator; for two outcomes, flip a coin.
Questions, answered
Can I roll a d20?
Yes. Pick d20 under Sides. Each face from 1 to 20 has a 5% chance.
How many dice can I roll at once?
From 1 to 100 dice per roll, all with the same number of sides.
Can I add a bonus to the roll?
Yes. Type it in Add to the total, positive or negative. The total includes it and the breakdown shows it.
Are the rolls fair?
Yes. Each die comes from the computer's cryptographic random source, with no face favoured.
Can I roll different dice together, like 1d8 + 1d6?
Not in one roll. Roll each set and add the totals; the history keeps both.
Is the history saved?
The last 50 rolls stay while you use the tool, and Copy puts them on the clipboard. They are not kept after you leave it.
Dice roller, and 16 more apps.
Download for Windows7 days free, then from $3.99 a month for all 17 apps. Windows 10 and 11.