Some board games use special proprietary dice. They're fun because they can emphasize the game's theme. However, dice can also be easy to misplace, and sometimes you lose the dice you need to play a game. Here's how to convert special dice to normal dice for your board games.
Option 1: Numbers instead of pictures
Specialty dice are useful because there's nothing clearer than a little sword icon when you roll a dice to attack your opponent, or a little picture of a shield when you roll to defend. But regardless of what iconography a die has on its sides, it's still just a die. Like any die, it represents the percentage of the chance to get one result out of many.
- Find a die with the same number of sides as your custom die.
- Count the number of times each icon on the custom dice appears. For example, an 8-sided die in Mansions of Madness features 3 Success (star icon), 2 Clue (magnifying glass icon), and 3 Fail (no icon) sides. Those are the Potential Results.
- Assign number ranges on your normal die to each Potential Result. For example, for Mansions of Madness 1-3 can serve as Star sides, 4-5 for Clue, and 6-8 for Fail sides.
You don't have to "map" the icons on the Special Die to specific numbers on your normal die. If you compare the Mansions of Madness die with an 8-sided die you buy from a gaming store, you might think that a Success matches up to the 1, a Clue to 4, Fail to 7, Success to 6, and so on. That's a purely aesthetic choice. A specialty die is designed so that when you look at it from any given angle, you see variety rather than a cluster of the same result. It looks and feels more random that way, but probability isn't affected by appearances. Just assigne number ranges to each result, and the probability remains the same.
Here's another example. The six-sided dice in Blackstone Fortress has 1 Success, 1 Critical Success, and 4 Fails. You don't have to be a probability expert to detect that the chances of rolling a success (critical or otherwise) is slim on this die, with just two chances compared to four opportuniies to Fail. On a normal six-sided dice, 1 becomes Success, 2 becomes Critical Success, and 3-6 are Fails.
Simple!
The Fallout board game features some complex specialty dice that contain results for both you and your enemies. To account for that, you have to roll two different sets of normal dice: one set of normal dice for the hits you deal to your enemy, and one set of normal dice for the hits your enemy has dealt to you.
Option 2: Random table
You can write down the results of a specialty die in a list (a "random table" in RPG terminology) and then use any die, with an equal number or more sides as there are items in the list, to choose a numbered item. If you use a die with more numbers than there are items on the list, just re-roll until you get a valid number.
Here's an example using Mansions of Madness again (with 3 Success, 2 Clue, and 3 Fail sides):
- Success
- Success
- Success
- Clue
- Clue
- Fail
- Fail
- Fail
Roll a normal 8-sided dice and see what the number you rolled translates to in the list. Or roll a 10-sided dice, but re-roll on a 9 or 10. Or a 20-sided dice, but re-roll on 11 or above (or treat 11 as 1, 12 as 2, and so on, re-rolling only on 17 or above).
Option 3: Percentages
If you happen to enjoy maths, then you can extrapolate the percentage of chance from a specialty die and "map" it to lots of other dice. If you don't enjoy maths but need to do this anyway because you happen to not have an equivalent normal die for your missing specialty die, then don't worry, this isn't calculating probability, it's just percentages and there's an easy way to check your work at the end. What you need to do using this method is calculate the percentages of results on the specialty die, and then formulate a near-equivalent on your normal die. Here are a few examples, starting with a simple imaginary one.
Simple Example
Suppos you have a game with a 4-sided die, with 1 Success icon, 1 Critical Success icon, and 2 Fail icons. To calculate the percentage of each icon, you take the number of each icon on the die and divide it by the total number of sides.
- Success: 1 divided by 4 = .25 (that's 25% but you can keep it as a decimal)
- Critical: 1 divided by 4 = .25 (25% but it's OK to keep it as a decimal)
- Fail: 2 divided by 4 = .50 (that's 50% but you can keep it as a decimal)
Check your work by adding up the numbers you calculated. Assuming you've done the maths correctly, you get 1.
.25 + .25 + .50 = 1
The final step is to figure out how to get those same percentages on some other die. The beauty of this method is that you can use any dice the same size or larger as the specialty die you're replacing. You don't need the same die. (The flaw in this method is that sometimes the percentages have to be cheated a little.)
To find the percent-value of each side of a die, divide 100 by the number of sides.
- 20-sided: 100 ÷ 20 = 5%
- 10-sided: 100 ÷ 10 = 10%
- 8-sided: 100 ÷ 8 = 12.5%
- 6-sided: 100 ÷ 6 = 16.6%
- 4-sided: 100 ÷ 4 = 25%
- 3-sided: 100 ÷ 3 = 33.3%
- 2-sided: 100 ÷ 2 = 50%
For this fictional example game, you could use a 20-sided or 8-sided dice as a substitute without changing the percentage of results.
- 20-sided (5% each side): 1-5 Success, 6-10 Critical, 11-20 Fail
- 8-sided (12.5% each side): 1-2 Success, 3-4 Critical, 5-8 Fail
If you're not bothered by a little variance, then you can use any die larger than the one you're replacing, and just choose how you want to tip the scale. For example, maybe this Fictional Example game has been a little too easy. Use a 6-sided dice with a little more chance of Failure: 1 Success (16.6%), 2 Critical (16.6%), 3-6 Fail (66.4%). Or maybe that's too drastic, and you're happy to succeed roughly half the time, but you decide that a Critical Success ought to be kept rare: 1-2 Success (33.2%), 3 Critical (16.6%)), 4-6 Fail (49.8%).
It's up to you, but once you know the percent-value of your specialty die and for each side of a normal die, you can map the value easily.
Mansions of Madness
This game uses an 8-sided die with 3 Success (star icon), 2 Clue (magnifying glass icon), and 3 Fail (no icon) sides.
To calculate the percentage of each icon, you take the number of each icon on the die and divide it by the total number of sides.
- Success: 3 divided by 8 = .375 (that's 37.5% but you can keep it as a decimal)
- Clue: 2 divided by 8 = .25 (25% but it's OK to keep it as a decimal)
- Fail: 3 divided by 8 = .375 (that's 37.5% but you can keep it as a decimal)
Check your work by adding up the numbers you calculated. Assuming you've done the maths correctly, you'll always get 1.
.375 + .25 + .375 = 1.0
Here are the percentages for relevant standard dice:
- 20-sided: 100 ÷ 20 = 5%
- 10-sided: 100 ÷ 10 = 10%
To get near to the original 37-25-37 split, you could use a 20-sided dice: 1-7 Success (35%), 8-12 Clue (25%), 13-20 Fail (40%).
You can work in 5% increments, so you can swing the game a little closer to Success by "stealing" a number from Fail: 1-8 Success (40%), 9-13 Clue (25%), 14-20 Fail (35%).
Or you can use a 10-sided die: 1-3 Success (30%), 4-5 Clue (20%), 6-10 Fail (40%).
Blackstone Fortress
This game uses a 6-sided die with 1 Success (Triangle), 1 Critical Success (Double Triangle), and 4 Fails (Blank).
The percents don't add up to 1 exactly, but that's because some of the numbers aren't evenly divisible. Here's the verification:
.166 + .166 + .666 = .998
So you need a 16-16-66 split, more or less. There are lots of options:
- 20-sided (5% sides): 1-3 Success (15%), 4-6 Critical (15%), 7-20 Fail (70%)
- 10-sided (10% sides): 1-2 Success (20%), 3-4 Critical (20%), 5-10 Fail (60%)
- 8-sided (12.5% sides): 1 Success (12.5%), 2 Critical (12.5%), 3-8 Fail (75%) or 1-2 Success (25%), 3 Critical (12.5%), 4-8 Fail (62.5%)
Option 4: Custom dice app
It's the 21st century and the Internet exists. You can use a Custom Dice Roller to create dice with custom sides. The site I'm pointing to from this blog post only allows you to label sides so, for example, instead of a cool sword icon, you have to settle for the word "sword".
Option 5: Buy replacement die
Sometimes the easiest way to replace die is to replace die. Many games sell replacement or additional specialty dice. Visit your friendly local game store to find out whether you can order more specialty dice.