jaybird,
Since Slowmodem handled that one rather quickly....Let me try and anticipate your next question.
Traditionally, each of these three sizes are made to hold 10 frames. However, a new trend that some have gone to is using boxes made to hold 8 frames instead of 10. This gives you a little more weight savings for lifting and "some" believe that the narrower width doesn't require as much encouragement to get the bees to draw out the end frames.
To further confuse the issue...Some people will shave down their frames to fit an extra in the brood box, while using one less in the honey supers to get thicker, easier to uncap in their opinion, comb.
So, someone using traditional 10 frame boxes might have 11 frames in the Brood boxes and 9 in the Honey supers. While someone using 8's might run 9 frames and 7 respectfully.
Currently, I use 8 frame mediums for everything, brood and honey supers, and actually use 8 frames in each.