A medium is 2/3 of a deep. 3 8 frame mediums is 24 frames. 2/3 of 24 is 16. Three mediums would be equal to 16 deep frames, or 1.6 deep 10 frame hives.

NOW, the number of frames is inmaterial. You need to go by weight. If you can weigh an empty 8 frame box, multiply by three, and add the weight of the top and bottom, then add 40 lbs. for stores. That should be the minimum your hive weighs going into winter in Tn.