<p>I know that bachelor's degree is the one you get after four years as an undergrad. I think master's is what you get when you go to a grad school for two years. How do you get a PhD and how long does it take? How hard is it?</p>
<p>The site: USNEI-Structure</a> of U.S. Education - Graduate/Post Education Levels has some helpful information.</p>
<p>For example: "The number of years required to complete a U.S. research doctorate vary by subject as well as by whether the student pauses during the program or continues straight through to the end. The median time lapse from earning a bachelor's degree to earning a research doctorate, for students remaining registered, is (in academic years):</p>
<p>for academic disciplines:</p>
<p>Humanities--Nearly 8 and one-half years;
Life Sciences--Seven years;
Mathematics--Nearly 7 years;
Physical Sciences--Nearly 7 years;
Social Sciences/Psychology--Seven and one-half years;</p>
<p>and for professional and applied fields:</p>
<p>Business and Management--Over 7 years;
Education--Over 8 years;
Engineering--About 6 and one-half years; and
Other Professions--Over 8 years.</p>
<p>The median number of registered years for all fields is just over 7 years. This means that, when added to the average of 4-5 years for a bachelor's degree, U.S. citizens who earn an American research doctorate have spent around 11 or more academic years in school as full-time students and researchers. During that time they are in structured and supervised programs, not on their own, and they do not benefit from government stipends or from any legal privileges permitting them to enjoy protected student status."</p>