The Yale Law School Career Development Office has a great post which calculates the number of hours an associate must work each day in order to meet the billable hour expectations of most law firm. What the spreadsheet shows from my point of view is that the only way to meet those expectation is to engage in creative if not fraudulent billing practices (although that is not the intent of the author who merely wants to help associates understand what to expect).
There is a great disclaimer at the bottom of the calculations, none of which actually explain how an associate legitimately reaches the hourly goals:
BUT once again this schedule does not account for any personal calls at work, training/observing, talking with coworkers, a longer lunch (to exercise? Christmas shop?), a family funeral, any pro bono work (if not treated as billable hours), serving on a Bar committee, writing an article for the bar journal, interviewing an applicant, etc.
I would add that the Yale calculations assume that every hour that is in fact worked gets billed whether it added value to solving the client's problem or not. We all know that many firms could care less about the value of the hour spent which creates a major conflict of interest with the client's goals.
I once knew a lawyer who used to quip about associates "We can put a monkey in that chair and get them to 2000 hours." I always believed that particular quote really captured the anti-client business model of most hourly billing firms.
How is it that many firms seem to bill at a rate of 100%-140% of the time they actually put in at the office? Associates are effectively forced to bill on their timesheets 10-12 hours per day by inflating the hours actually worked. They are under tremendous pressure to charge a minimum 12-18 minutes for work that may take 1-5 minutes worth of time. They bill for everything they do, whether administrative or otherwise (ie transmittal letters). And of course, they are under pressure to always round minutes upwards.
Here is a good discussion thread on what a reasonable billable goal is, measured about how much time you actually work. There is discussion that suggest you are efficient if you bill 40% - 70% of the time you actually put in at the office.