All grain brewing is a little trickier. You should know what your pre-boil volume needs to be, and you should be able to calculate what your pre-boil gravity should be. With these 2 numbers in hand, after the mash you should know that you want 6.5 gallons of 1.045 wort and that after the boil, you will have 5.5 gallons of say 1.052 wort (not exact). Sometimes, you need to add water or DME pre-boil to get the right numbers or even add some water post-boil...or just accept that your beer is going to be a little stronger.
Draft 3: Belgian Dubbel
Primary 1: German Hefe