Free Dice Roller & Odds Calculator
Type dice notation to roll it, see the exact odds of every total, and find your chance of beating a target.
What is a Dice Roller & Odds Calculator?
This dice roller reads standard tabletop dice notation, rolls it for you, and works out the exact chance of every total. It handles sums like 2d6+3, keep and drop such as 4d6 drop lowest or advantage, percentile and Fate dice, exploding dice and targets.
Add a target such as >= 15 to get the chance of success, the number most players want before rolling. Odds are exact, not simulated: dice are combined total by total, keep and drop rolls are worked out from every possible outcome, and exploding dice are followed five rerolls deep.
Key Features
Full Dice Notation
NdX, d%, dF, constants, plus and minus.
Keep and Drop
Advantage, disadvantage and 4d6 drop lowest.
Exact Odds
The chance of every total, and of reaching it.
Target Chances
Add >= 15 to see your chance to succeed.
Roll History
The last ten rolls, with dropped dice struck through.
Perfect for everyone
- Tabletop roleplayers
- Game masters
- Board gamers
- Game designers and teachers
How to Use the Dice Roller & Odds Calculator
Type the dice the way a rulebook or character sheet writes them, or choose a common roll from the list. The Roll view rolls them as often as you like, while Chances and Stats show the odds behind every roll, so you can see whether a bonus or a different die is worth it.
Type the Dice
Such as 2d6+3, or pick a common roll.
Add a Target
Add >= 15 to get the chance of success.
Roll
Press Roll; dropped dice show struck through.
Read the Odds
Chances lists every total; Stats sums it up.
Rolls, Worked Out
Each row is a roll from tabletop games, from a d20 attack to a Fate skill check, including a couple of typing slips. Each answer is this tool’s odds, stats or check, worked out exactly rather than by rolling many times, so the same notation always gives the same figures.
“1d20+5 >= 15”
“4d6dl1”
“2d20kh1”
“2d20kl1+5 >= 15”
“4dF+2”
“8d6”
“1d6!”
“2d6”
“3d6kh4”
“2d6+”
Dice Notation
Dice notation writes a roll as the number of dice, a d, and the number of sides, with extras for keeping, dropping and exploding. This is the notation this roller reads, which matches what most virtual tabletops accept. Spaces are ignored and letters can be upper or lower case.
NdX
Roll N dice with X sides and add them; d20 means 1d20.
“What does 3d8 mean?”
+ and −
Add or subtract dice and numbers, as in 2d6+1d4−1.
“Can you subtract dice?”
d%
Percentile dice, from 1 to 100.
“What is d% short for?”
dF
A Fate die: −1, 0 or +1.
“What range does 4dF cover?”
khN and klN
Keep the N highest or lowest dice.
“What is advantage?”
dlN and dhN
Drop the N lowest or highest dice.
“What is 4d6dl1?”
!
Explode: roll again and add when a die shows its top face.
“When does a d6 explode?”
>= N
Compare the total with a target to get the chance of success.
“What does >= 15 add?”
How the Odds Are Worked Out
Every number on this page is exact. Nothing is estimated by rolling thousands of times, so the chances add up to precisely 100% and match what the dice really do over many rolls.
One Die
Each face of a fair die is equally likely: 1 in 6 on a d6, 1 in 20 on a d20.
Adding Dice
Two dice are combined by pairing every face of one with every face of the other, which is why middle totals are more common.
Keeping and Dropping
Every possible roll of the whole group is listed and sorted, then the kept dice are added up.
Exploding Dice
Each explosion adds another roll on top; the odds follow five explosions per die.
Common Rolls Explained
Some rolls come up in almost every session. Knowing their odds helps players decide when to take a risk and helps game masters set fair targets, and each one below can be checked in the Stats view.
1d20 Against a Target
Each +1 bonus adds 5 percentage points to the chance of success.
Advantage
2d20 keep highest averages 13.8 instead of 10.5.
Disadvantage
2d20 keep lowest averages 7.2.
4d6 Drop Lowest
The standard way to roll ability scores, averaging about 12.2.
2d6
7 is the most likely total, a sixth of all rolls.
Reading the Odds
How to use the chances and stats views to make better decisions at the table, or when designing a game. The same few habits answer most questions about whether a roll is worth making.
Use At Least
The at-least column is your chance to reach a total or more.
Compare Bonuses
Change +5 to +7 and watch the target chance move.
More Dice, Less Swing
3d6 clusters near the middle more than 1d18 does.
Average Isn’t Typical
Exploding dice have long tails that pull the average up.
Check Before Designing
Make sure a target is possible before writing it into rules.
Setting a Target
Add a comparison to the end of the notation and the Stats view gives the chance of success alongside the usual numbers. It works with every kind of roll, from a single d20 to a pool with dice dropped.
>= and >
Meet or beat a number, as for armour class, difficulty classes and most skill checks.
<= and <
Roll under a number, as for percentile skills or games where low is good.
Impossible and Certain
The check warns when a target can never be reached or can never be missed.
How Keep and Drop Change the Odds
Rolling extra dice and setting some aside is a simple way to make results better, worse or more reliable, and it changes the shape of the odds as well as the average. The Chances view shows the full curve for any of these.
Advantage
Keeping the higher of two d20s lifts the average by over three points and doubles natural 20s.
Disadvantage
Keeping the lower does the opposite, making high totals rare.
Drop Lowest
4d6 drop lowest skews ability scores upward and makes 3s very rare.
Dice Pools
Keeping a few dice from many favours high totals more as the pool grows.
Dice Notation Pitfalls
Small typing slips that quietly change a roll, or stop it from being read at all, usually found mid-session at the worst moment. The check view reads the notation back in words, which is the quickest way to confirm a roll means what you intended.
Keep vs Drop
kh1 keeps one die; dh1 drops one, which isn’t the same on 3 dice.
Missing Signs
2d6 3 isn’t read; write 2d6+3.
Too Many Kept
You can’t keep more dice than you rolled.
Exploding and Keeping
Pick one; together they’re ambiguous between games.
Huge Pools
Very large keep rolls have too many outcomes to count exactly.
Dice in Popular Game Systems
Different games build their rules on different rolls, and the notation covers all of the common ones. These are typical examples of what players type into a roller for each style of game.
d20 Games
Roll 1d20 plus a modifier against a target number, with advantage and disadvantage in fifth edition.
Fate
4dF plus a skill against a difficulty; results cluster tightly around zero.
Savage Worlds
Trait dice explode on their top face, a rule the game calls aces.
Powered by the Apocalypse
2d6 plus a stat, where 10 or more is a full success and 7 to 9 a partial one.
Percentile Games
d100 rolled under a skill, as in many horror and historical games.
Who Uses a Dice Roller
Anyone who needs dice without a bag of them to hand, or who wants to know the real odds before committing to a roll. It works on a phone at the table as well as on a laptop during prep.
Players
Roll attacks and checks when dice aren’t at hand.
Game Masters
Set targets that are hard but possible.
Game Designers
Balance abilities and items by their odds.
Board Gamers
Settle how likely a roll really is.
Teachers
Show probability with a familiar example.