"Can somebody recommend a probability calculator for..." Topic

What I'd like is a nice little calculator that gave me the odds of rolling at least one X or X-or-better score, on Y number of dice.

For example: Let's say I roll four d6s. What are the odds of scoring at least one 6? What are the odds of scoring at least one 5+? At least one 4+ ? and so on.

I'd like to be able to fool around with it, changing the number of dice rolled, and also changing the target.

But in every case, the outcome would be: the odds of scoring at least one instance of Y. (In other words, it doesn't matter how many successes are scored… only whether at least one success is scored.)

thanks,

Sam

That's a pretty easy one – you just multiply together the chance of failure on each dice to get the chance of *failing* to score any successful rolls. Subtract that from one, and you've got the chance of at least one success.

Eg. 4 dice needing a 6, the chance of failure is .8333 x .8333 x .8333 x .8333 = .48, so a 48% chance of no sixes, which gives a 52% chance of at least one.

anydice.com

--
Martin Stephenson
The Waving Flag :: Twitter :: eBay

You can set up a cross reference spreadsheet in minutes. Mail me if you want it. That solves having to always go back and recheck each result.

pygmywars @ gmail.com

As previously mentioned: anydice.com

I got curious how to use anydice.com , couldn't follow the online documentation. Finally I googled up some discussions on RPG.net.

Anyway to calculate 4 dice needing a 6, put it into anydice.com this way:

output [count {6} in 4d6]

Here's the result in the Export button format:

"output 1",0.666666666667288,0.7453559925002131,0,4
#,%
0,48.225308642  <-- answer
1,38.5802469136
2,11.5740740741
3,1.54320987654
4,0.0771604938272

So the answer is 48.225% of no 6s, meaning 51.775% of at least one 6.

I would recommend doing it yourself by hand (well, with a spreadsheet). If you want to develop and design a ruleset, you should understand not just what the answer to XYZ question about the mechanic you are considering is, but you should also understand why it is that way.