That's normal and I consider myself very productive. But here's the real question, how do you present this info to clients/bosses/entrepreneurs without them throwing a big hissy fit?
This is a big problem when working with people who are heavily and directly invested in the business you're helping because they feel like they're productive 12+ hours a day and feel that you should be too. Most of the time they're just fooling themselves, or their idea of productivity is so different from an engineer's that it's nearly impossible to compare.
Furthermore, so far everyone I've said "Dude, you're not even half as productive as you think" to directly got grossly offended by my suggestion.
I've been trying to get to the bottom of these for a year and a half now (writing a book about this stuff) and I can't say I'm much closer to a solution.
PS: the worst part of this equation is that you're often asked to look productive for 8 or 9 hours a day because that puts people at ease. That makes them feel they're paying you fairly, even though you could easily do the same amount of actual focused work in 7 hours and spend the rest of that time doing other things.