A Weighted Grade Calculator

The formula this calculator uses

course grade = score1 x weight1 + score2 x weight2 + ...

score

The percentage earned in a category

weight

That category's share of the course grade, as a decimal

grade

The weighted course grade

sum of weights

Must come to 1.00, or the division that follows corrects for it

How to check the result by hand

1. 1

   List every category with its score and its weight

   Copy the weights from the syllabus rather than from memory, and check that they add up to 100 percent. Four categories weighted 20, 15, 25 and 40 give exactly 100, which means no division is needed at the end.

2. 2

   Convert each weight to a decimal

   Twenty percent becomes 0.20 and forty percent becomes 0.40. Forgetting this step is the most common error, and it inflates the answer by a factor of a hundred while still looking like a plausible grade.

3. 3

   Multiply each score by its weight

   Eighty five times 0.20 is 17, ninety times 0.15 is 13.5, seventy eight times 0.25 is 19.5, and eighty eight times 0.40 is 35.2. These contributions are the category's share of the final grade.

4. 4

   Add the contributions

   17 plus 13.5 plus 19.5 plus 35.2 comes to 85.2, which is the course grade. If the weights added to something other than one, divide by their actual total at this point.

5. 5

   Compare against the unweighted average

   The plain average of 85, 90, 78 and 88 is 85.25, so the weighting moved the grade down by 0.04999999999999716. The direction tells you whether the heavier categories are your stronger or weaker ones, which is the most useful thing the comparison reveals.