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, Orange Blossom Mead, Fat Man Porter
Primary:sLambic I, Janet's Brown
Secondary: Toasted Caramel Port, Flanders Red
Kegged: Hefeweizen, Centurion Falcon IPA< Dark Saison
2013 dump volume: ~2 gallons