I noticed recently one of the feedback stats on the stationary bikes at the YMCA is something called METs, and I had no idea what it meant. Apparently, and MET is a "metabolic equivalent". One MET is the amount of energy you use just sitting quietly. Walking is 2.5 METs. That is, it uses 2.5 times as much energy as sitting around. Playing raquetball uses 12 METs.
Now that I know this unit exists, I thinking I'm going to be estimating my METs constantly. As I sit her typing, I'm using 2.3 METs (assuming it's the same as playing the piano). I'm about to walk home which should bump it up to about 3.3 METs. Then I have to make cookies. Maybe 2.5 METs? And so forth.