How Many Credits Do You Need to Graduate From High School?

High school diploma requirements vary from state to state, with most states requiring between 18 and 24 credit hours for graduation. Some states have increased their requirements in response to research that shows that many high school graduates need remedial courses to succeed in college. Some states have more than one level of diploma that can be earned. In the second decade of the 21st century, many states' requirements are shifting rapidly as they adapt to federal education policies and new theories of effective teaching. You'll need to check your state's department of education for specific requirements.

Credits in high school education are measured by the Carnegie unit system, which was developed around the turn of the 20th century by the Carnegie Foundation for the Advancement of Teaching. One Carnegie "hour" equals 120 hours of classroom time with an instructor, or five hours a week for a half-year semester. Critics of the Carnegie say it places too much importance on the amount of time students spend in a classroom without assessing what they may or may not have actually learned.

All states require instruction in math, English, science and social studies for students to graduate, but how many years of each and which courses are offered vary. Many states require four credits of a core subject: two or three years of core instruction and one or two more credits that can be earned in optional advanced placement or career and vocational courses in that subject area. In Texas, for example, core requirements state that students must earn four English credits; they must pass English I and II but can earn the last two credits by choosing among options such as journalism, literature, business English and creative writing.

Some states require students to pass exit examinations to receive a high school diploma. These may be given at different levels to students with different needs; New York offers a Regents Competency Test as a safety net provided to students who cannot pass its traditional Regents exams. California students must pass the California High School Exit Examination and are given multiple opportunities to take it beginning in grade 10.

As educators strive to ensure that high school graduates are prepared for education or the workplace, some school districts are turning to a proficiency-based approach to graduation requirements -- one that depends on a student's ability to prove what she knows through detailed assessments rather than awarding a diploma based on hours spent in a classroom. Proficiency tests can include written tests, oral examinations or other tasks. Maine and Hawaii have both instituted high school graduation requirements based on proficiency.

In every state, students who are unable to graduate from high school by accumulating credit hours or passing proficiency assessments can take a GED, or high school equivalency exam -- a multiple choice test that measures a basic grasp of core-subject knowledge. The system was developed to offer a route to a diploma that made sense for returning World War II veterans. A GED is not considered a true equivalent of a standard high school diploma, but it is accepted for admission at many community colleges, where remedial courses are also offered to make up for deficiencies in learning.