I was just wondering how most people calculate their efficiency? Isn't there an easier way to figure your efficiency from your pre-boil gravity reading? This is really what we want to know right? The extraction % from the grain, that is.
You can use the numbers 'into the kettle' or 'into the fermenter'. I call the 'into the kettle' numbers the mash efficiency and the 'into the fermenter' numbers the brewhouse efficiency. I tend to use brewhouse efficiency because that tells me how much grain I need to hit a certain OG in the fermenter (makes it easier to formulate recipes for my system). Many people use efficiency into the kettle. Either way works they are just a little different. If you know your 'boil efficiency' then it's easy to relate the two.
You will suffer a small efficiency loss in the kettle (boil efficiency). When you measure the volume in the kettle, the break volume is included in that. Then you'll add hops which will absorb some wort as well as displace some volume, some/most of that will be left behind in the kettle. Depending on how much trub/break/hops there are and how much make it into the fermenter will affect the boil efficiency.
I measure the volume and gravity into the kettle just to make sure I'm on the right track to hitting my target OG into the fermenter, but I never calculate my efficiency from those numbers (but lots of folks do). After the boil/chill I fill the carboy, then I strain any leftover wort into a gallon jug and freeze it for yeast starters (I intentionally make the batch a quart or two more than I plan to put in the fermenter). So I always know exactly how much wort I got (even though it didn't all go into the fermenter) and know the gravity.
Try both ways and see which you prefer. Just keep in mind that if you brewed two identical batches except one had 1 oz of pellet hops and the other had 6 oz of leaf hops, your boil efficiency will be different thus the brewhouse efficiency will be different. But the mash efficiency will be the same. Another reason I tend to use brewhouse efficiency.