I built a spreadsheet to calculate mash efficiency. I just brewed my stout. Let me know if this is right.
8 lb 2 row
1.5 lb crystal 80
1 lb chocolate
.5 lb roasted barley
1 lb flaked oats
Mash resulted in 8.75 gallons wort @1.043 gravity. My spreadsheet tells me that's 93.5% eff, I don't mean to brag but f it's right... yeah me!