You may want to look at Devan Rawn's quantifying on using a single (10-frame deep) brood chamber. He goes into the numbers bigtime in this 11 minute YOUTUBE video:Thanks Jack. That's helpful. I think I've erred on the side of giving too much space since I started keeping bees. I'm not motivated by efficiency so I have not done this kind of quantifying before. That's good!
This year I am trying to use 2 7-frame mediums as a brood chamber with a QE on top. It may be too little space.