Its a tough one to estimate. There's the 8 hour job in there, but does one really spend those entire 8 hours looking at the screen? What about breaks? Lunch?

Its a tough one to estimate. There's the 8 hour job in there, but does one really spend those entire 8 hours looking at the screen? What about breaks? Lunch? Meetings? Taking out sleep, cooking/eats (assuming not eating looking at the screen), reading (assuming not read from a screen), physical activities, hobbies, holidays, travel, etc and the number should go down a bit. Of course, if you watch TV, use a tablet, a kindle, and don't do anything else, then the number suddenly goes up. I settled on 10. 8 hour job. Don't watch TV, prefer real books, but end up programming on the bus and a few hours after work. Which is probably too much for a physically healthy human life. Need to do something about that...