Collegiate calendars
Three calendar systems are used by most American colleges and universities: quarter system, semester system, and trimester system. These are ways the calendar year, measured September–August or August–August, are organized into a formal academic year. Some schools, particularly some business schools and community colleges, use the minimester or mini-semester system.
The quarter system divides the calendar year into four quarters, three of which constitute a complete academic year. Quarters are typically 10 weeks long so that three quarters amount to 30 weeks of instruction. Approximately 20% of universities are on the quarter system.[3]
The semester system divides the calendar year into two semesters of 15 weeks each, plus optional summer sessions of varying lengths. The two semesters together constitute 30 weeks of instruction, so that three academic quarters equal two academic semesters. Thus, academic credit earned in quarter hours converts to semester hours at 2/3 of its value, while credit earned in semester hours converts to quarter hours at 3/2 of its value. Or, to put it another way, 3 quarter hours = 2 semester hours, and 2 semester hours = 3 quarter hours.
In practice, the average quarter course is 4 or 5 units and the average semester course is 3 units, so a full time student graduating in four years would take five courses per semester and three or four courses per quarter.
Some colleges and universities, such as Berea College, MIT, UMass Amherst, Calvin College, Williams College, Linfield College, Oberlin College, Middlebury College, UMBC, Eckerd College, Wofford College, Austin College, Samford University and Colby College, have a 4-1-4 system, which divides the year into two four-month terms (September to December and February to May) as well as a single one-month term in January in which students can do independent study, study abroad, internships, activities or focus on a single class. The one-month term is sometimes called a mini-mester.
The trimester system evolved out of the semester system. It divides the academic year into three equal portions of 10–11 weeks each. Institutions that use the trimester system include the University of Michigan, Lawrence University, and Carleton College. The fall and winter and spring trimesters constitute an academic year of 30–32 weeks.[4] The reduced maximum course load that accompanies the shortening from the traditional semester makes the trimester system compatible with the semester system. Academic credit is thus measured on the trimester system in semester hours; there is no such thing as a "trimester hour" of credit.