is there a chart, calculator, or formula to figure out what your starting gravity is after mashing to figure out to what volume you will need to end with? Do you guys take a gravity reading after mashing?

for example:i mash my grains and have 7 gallons of wort at 1.021 and my recipe calls for an OG of 1.054... Someway/ thing to tell me I need to boil till I get to 5.5 gallons to reach my OG?

also woukd be helpful using a recipe that assumes a certain % efficiancy and I don't know what mine will be

thanks,

sean

(im guessing once I reach a consistent efficiancy I will know but just starting out I have no idea)