You should just go with Mr. Master Electrician's advice above. I broke out Marks Standard Handbook to see if I could dig up some EE #s. Sure enough, there's a little section on wire sizing.
A = 21.6*I*d/e where A is area needed in cir mils. 21.6 accounts for the resistance in copper wire...
I'll take it a step further and say those converters are a terrible idea. They're not a solution to your problem.
Unless you really need to brew and do laundry at the same time, seems to me your problem isn't that you need to split the dryer circuit, you just need to be able to more easily...