If those calculators the previous posters suggested still don't work for you, you can use your boil kettle to mash in. Being able to direct-fire your mash tun allows you to easily hit your desired temperature. If you don't have a screen or false bottom in your kettle, just pour the whole mess into your cooler mash tun after 60' for lautering and sparging. I frequently do this when I step mash or do a hybrid step-decoction mash, and never had any problems.
The Fiesty(sic) Goat Brewery est. 2007 & Clusterfuggle Experimental Ales est. 2009
Planned: sLambic II, Flanders Red II
Primary: Fat Man Porter, Orange Blossom Mead, sLambic I
Secondary: Flanders Red I
Kegged: 3 different ciders, Janet's Brown, Barrel-aged Stout, Hallertau Blanc Pale Ale
Bottled: Flanders Red I