Here is a link a Dungeon Assault Calculator. Click the link, you will be asked to download it; it's on an external site, and completely free of viruses (I promise!). This program wasn't JaGEx's idea, it wasn't sponsored by them, nothing. It's also important to note that since JaGeX refuses to release the actual formulas for the game, the formulas powering this program can't be guaranteed 100% accurate - don't bet your life on it.
Since it's in beta, several raiders are missing. A few of them are missing. I think they are: Berserker, Dark Knight, Zealot, and Ranger of the North. But I'm pretty sure all the dungeon rooms are there. If you have a glitch, or you get a result that makes no sense, or you don't understand something about the program, please say so here.