Flipping Coins: Dice for a Desert Island

If you’re like me, you’ve had those times when you’re at your Grandfather’s for Xmas, and your younger cousin who’s really curious about this whole “roleplaying thing” wants you to run a game for her, but you try to weasel out of it by saying you don’t have any dice, and of course she’s like well why’s that important and doesn’t understand why you won’t run something, until finally you accept your filial duty and run a pickup game hunkered in a corner of an upstairs hallway where the rest of the relatives won’t notice, but eventually they hear the weird cawing noises you make when the intrepid wizard and her sneaky companion creep through the crow-infested orchards outside the ruined castle on the way to find the lost crown of their forgotten kingdom.

It could happen to you. It could happen to anyone: you want to game, but you have no dice.

What do you do? Flip a coin, or maybe a bunch.

Heads, Tails, Criticals

Any range of numbers you could roll can be easily represented with a bunch of coins. The more coins you use, the more fine-grained the result.

It’s easy: divide the size of your die by the number of coins you are going to flip. Flip your coins, and multiply the number of heads you get by the result to find your roll. Zero heads equals the lowest value (a 1 usually).

Let’s take the ubiquitous d20. If we use only two coins we divide 20 by 2 and get 10 for each coin, so if we get 1 head we get a 10, 2 heads is a 20, zero heads is a 1. A better spread is probably 4 coins (20/4 = 5), which gives us 1/5/10/15/20 for zero through four heads respectively. We could also go all the way up to 10 coins, whatever.

Want to do an odd range like 10-60 for that big fireball? Just treat the number range the same as a single die of that size. We’ll fudge and call that 0-50 + 10. On two coins that’s 10/35/60 (0/25/50 + 10). Or flip five coins and have each head do 10 more damage.

What are the odds?

Are the odds the same for flipping coins as rolling a die? Nope, not exactly. Without getting too technical, the more coins you flip the more of a bell curve you create, so the mid-range results will be more likely.

Interestingly if you use 4 coins to recreate a d20, you have a 1 in 16 chance of either a 1 or a 20, which is pretty close to the normal odds. So feel free to let someone get a critical if they flip four heads, or hit them with a house rule fumble if they get all tails.

Now go forth and teach your relatives how to game. You have one less excuse.

    Ben Robbins | December 27th, 2007 | game design | show 8 comments