How do I calculate a grade with points?
In a points class, every point counts the same. Add up all the points you earned, add up all the points you could have earned, and divide the first by the second. Here is a class with four graded pieces of work:
- Homework 1: 18/20
- Quiz 1: 42/50
- Lab report: 27/30
- Unit test: 81/100
Points earned: 18 + 42 + 27 + 81 = 168. Points possible: 20 + 50 + 30 + 100 = 200. The grade is 168 ÷ 200 × 100 = 84%, a B on a plus/minus scale.
Notice that the unit test, worth 100 points, pulls the grade down more than the others. That is how a points class works: bigger assignments count more because they have more points.
How do I calculate a weighted grade?
In a weighted class, the syllabus gives each category a share of the grade. First find your average in each category. Then multiply each average by its weight, add the results and divide by the total of the weights.
- Homework: average 94%, weight 20%
- Quizzes: average 86%, weight 30%
- Tests: average 79%, weight 50%
94 × 20 + 86 × 30 + 79 × 50 = 8410. The weights add up to 100, so the grade is 8410 ÷ 100 = 84.1%, a B.
Tests are half the grade here, so a 79% in tests pulls the grade down even though homework and quizzes are higher. The weighted grade calculator averages each category’s scores for you.
What if the weights don’t add up to 100?
Partway through a term, some categories have no grades yet. Say the final exam is worth 20% and has not happened. The other weights then add up to 80, not 100: Homework 15%, Quizzes 25%, Tests 40%.
Divide by the weights you have, not by 100. 94 × 15 + 86 × 25 + 79 × 40 = 6720, and 6720 ÷ 80 = 84%. Dividing by 100 would give 67.2%, which is far too low: it counts the missing final as a zero.
How do I turn my grade into a letter?
Look up your percent on your school’s grading scale. On a 10-point scale, an A starts at 90, a B at 80, a C at 70 and a D at 60. A 7-point scale is stricter: an A starts at 93 and a B at 85. Plus/minus scales split each letter into three, so 87 to 89.99 is a B+ and 90 to 92.99 an A-.
Rounding matters at the edges. A grade of 89.5% is a B+ without rounding, but if your teacher rounds to the nearest whole number it becomes 90, an A-. Ask which rule your class uses.
What do I need on the final?
Use this formula: needed = (target − current × (1 − w)) ÷ w, where w is the final’s weight as a decimal. With the 84% above and a final worth 20% (w = 0.2), an 80% overall needs (80 − 84 × 0.8) ÷ 0.2 = 64% on the final. The final grade calculator shows the score you need for every letter at once.
What are the most common mistakes?
- Averaging percents in a points class. Here the average of the four percents is 86.25%, but the real grade is 84%.
- Dividing by 100 when weights are missing. Divide by the weights that have grades.
- Forgetting dropped scores or extra credit. Check the syllabus for “drop the lowest quiz” or bonus points.
- Missing work. A missing assignment usually counts as zero until it is handed in.