According to the US Department of Education, the median time lapse between earning a bachelor's degree and earning a PhD degree in the US is 8 and a half years in the Humanities and roughly 7 years in Mathematics, Physics, or the Life Sciences. These figures seem excessive, especially by international standards.
In the European Union for example, the standard time to complete a doctorate under the new 3B/2M/3D Bologna system is 5 years beyond an initial bachelor's degree . In certain fields, especially engineering and hard sciences, students usually take longer, but never more than 6 years counting from the year the bachelor's degree was awarded (government funding is normally discontinued at this point and degree-granting institutions are heavily penalized with a reduction in research funding if doctoral students do not graduate within a reasonable amount of time).
The most often heard explanation for the excessive time American students take to get a PhD is that, unlike their counterparts in Europe, doctoral students in the US are required to take a large number of graduate classes and prepare for a series of screening and qualifying exams in the initial years of the program before choosing a thesis topic. That same argument is sometimes used to suggest that US PhD programs are somehow "stricter" or "tougher" than equivalent doctoral programs in the European Union. That is however not exactly true.
First of all, in several European universities, especially in certain deparments in the UK, PhD students now do take classes (and associated final exams) in their first year in the program. Furthermore, it is standard practice in the UK for students coming into the program with a 4-year undergraduate degree (MSci, MEng, etc.) to enroll initially as Master of Philosophy (MPhil) candidates and then be promoted to PhD candidacy following an oral Transfer Exam. Still, they are able to complete the whole program in no more than 4 years beyond their initial undergraduate degree.
Second, although that may be controversial, the standard continental European opinion is that the American model of requiring extensive coursework and multiple preliminary exams from PhD students is just a way to compensate for the deficiency of both secondary and undergraduate college education in the US when compared to Europe. In other words, a French commentator would probably argue that a student who holds a "Licence" from a French university or an "Ing