It depends on exactly what you count as 'work', but if I count all the things I do for the sake of work that tie me to the computer (so counting e.g. the team's

It depends on exactly what you count as 'work', but if I count all the things I do for the sake of work that tie me to the computer (so counting e.g. the team's informal chat half-hour), then about 9 hours. If you count just mentally intensive work (writing/reviewing code, writing/reviewing designs, making plans), then it's hard to do more than 4-5 hours per day (in terms of how long I can focus - days usually don't have that much free time for "real" work!)