How this calculator works
A weighted average treats some scores as more important than others. Multiply each score by its weight, add the products and divide by the total weight. If the weights are 20, 30 and 50, the third score counts half of the final grade. Weights do not have to add to 100: 2, 3 and 5 give the same result as 20, 30 and 50 because the division cancels the scale. Points mode is the same idea when grades are recorded as earned out of possible, such as 18 out of 20, because the possible points are the weights.
Formula
percentage mode: grade = sum(score x weight) / sum(weight). points mode: grade = sum(points earned) / sum(points possible) x 100. Contributions shown in the table are each item share of the final percentage. The letter grade uses a standard scale: A+ 97, A 93, A- 90, B+ 87, B 83, B- 80, C+ 77, C 73, C- 70, D+ 67, D 63, D- 60, F below 60.
Worked example
Scores of 85 with weight 20, 92 with weight 30 and 78 with weight 50 give 1,700 + 2,760 + 3,900 = 8,360, divided by 100 weights = 83.6 percent. That is a B under the scale above. In points mode, earning 17 out of 20, 46 out of 50 and 39 out of 50 gives 102 out of 120, or 85 percent, also a B.
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Frequently asked questions
Do weights have to add up to 100?
No. Only the ratio between weights matters. Using 1, 2 and 2 gives the same weighted average as 20, 40 and 40. The total weight field reports the sum so you can check the assignment scheme.
What is the difference between percentage and points mode?
In percentage mode each score is already a percentage and the second number is its relative importance. In points mode the score is points earned and the second number is points possible, so the calculator adds all earned points and divides by all possible points. Use points mode when the assignment list shows marks such as 18/20.
Can I drop the lowest score?
Not directly. Remove that item from the list and adjust the total yourself, or enter it with a weight of zero in percentage mode. Many course outlines drop the lowest quiz; if so, leave it out of the list to match.
Why does my letter grade differ from my school report?
Schools use different percentage cut-offs. The scale here is a common one, but some schools start an A at 90 and others at 93, and some use plus and minus grades differently. The percentage is the part this calculator computes exactly; the letter is a convention.