I use a quart of heavy cream and end up with about 1/2lb. of butter (maybe a bit more) and a 1/2 quart of Buttermilk. I use a KitchenAide stand mixer and the first time I did it, I did not cover the bowl with a towel and walked away from the mixer for a few moments. I returned to buttermilk all over the place and spent about a half hour cleaning up the counter, floor and mixer.
The buttermilk can be cultured and used to make cheese creations or use it for biscuits or pancakes. YUMYUM!