Even though teachers can calculate grade scores in an almost infinite number of ways, some common themes for determining grades run through most educational institutions. Most schools have a grading scale, which is a set of standard percentages that shows what students must earn for each letter grade A through F. A student can then calculate the percentage she has earned in a class and compare it to the grading scale to figure out her letter grade. Many teachers will grade assignments as percentages, while some use straight point systems. Both systems will be taken into consideration here.

Calculating Grades from Straight Points

1. Add Up Total Point Values

Add up the point values of all of your graded assignments. For instance, you may have completed four assignments worth the following numbers of points: 10, 20, 20 and 30. If you add them up, you find that the assignments were worth a total of 80 points.

2. Add Up Your Scores

Add up scores that you earned on each assignment. For example, suppose that on the assignments from the previous step, you earned the following scores: 7, 19, 14 and 23 points. If you add them up, you get a total of 63 points.

3. Divide Scores by Total Point Value

Divide the total number of points you earned by the total point value of all the assignments, and then multiply the number by 100 percent. For example:

Percentage of points earned = 63 ÷ 80 x 100 percent = 79 percent

4. Interpret the Grading Scale

Compare your percentage to the grading scale to find your letter grade. For example, suppose your school's grading scale looks like this:

• A - 90 to 100 percent 
  
• B - 80 to 89 percent 
  
• C - 70 to 79 percent 
  
• D - 60 to 69 percent 
  
• F - less than 60 percent
  

Because you earned 79 percent of your points, you earned a "C."

Calculating Grades from Percentages

1. Add Up Percentages Earned

Add up the percentages you earned on all of your assignments. For instance, you might have completed four assignments and earned the following percentages on each: 78, 88, 94 and 81 percent. If you add them up, you get 341.

2. Divide by Number of Assignments

Divide your answer from the previous step by the number of assignments to learn your average percentage. For the example, the calculation would look like this:

Average percentage = 341 ÷ 4 = 85.25 percent

3. Interpret the Grading Scale

Compare your average percentage to the grading scale to find your letter grade. For example, suppose your school's grading scale looks like this:

• A - 90 to 100 percent 
  
• B - 80 to 89 percent 
  
• C - 70 to 79 percent 
  
• D - 60 to 69 percent 
  
• F - less than 60 percent
  

Because your average percentage was 85.25 percent, you earned a "B."