Weighted Average Calculator
Add value and weight rows to compute a weighted average, or flip to reverse mode to solve for a missing value.
Worked examples
Semester GPA from course credit hours
A student wants a weighted GPA where each course's grade points count in proportion to how many credit hours the course was worth, not just a flat average across courses.
- Course A
- 3.70 GPA × 3 credits
- Course B
- 4.00 GPA × 4 credits
- Course C
- 3.00 GPA × 2 credits
≈ 3.68 GPA weighted by credit hours
Weighted-average unit cost across purchase lots
A warehouse bought the same part in three lots at three different prices and wants a single weighted-average unit cost for accounting, so bigger lots influence the cost more than small ones.
- Lot 1
- 100 units @ $5.20
- Lot 2
- 250 units @ $4.80
- Lot 3
- 150 units @ $5.50
≈ $5.09 average cost per unit
How the formula works
Picture each value hanging on a beam like a weight on a scale — a bigger weight pulls the balance point of the beam closer to itself. The weighted average is exactly that balance point: multiply each value by its own weight, add those products up, and divide by the total of all the weights. Values with a larger weight end up counting more toward the final number, while a value with zero weight wouldn't move the balance at all.
Solving for a missing value works the same equation in reverse: multiply the target average by the total of every weight (including the unknown row's), subtract off the value×weight products you already know, then divide by the unknown row's own weight.
Frequently asked questions
What's the difference between a weighted average and a simple average?
A simple average treats every number equally, adding them up and dividing by the count. A weighted average lets some numbers count more than others by multiplying each one by its own weight before dividing by the total of the weights — so a course worth 4 credit hours pulls a GPA further than one worth 1 credit hour, even if both have the same grade.
How does the "check 2 or more rows" selection work?
Each row has a small checkbox. Leave zero or exactly one row checked and the calculator uses every row with both a value and a weight — the checkboxes are effectively off. Check two or more rows and the calculator switches to averaging only that subset, which is handy for pulling a weighted average out of a larger list without deleting or retyping anything.
Can I solve for a missing value instead of computing the average?
Yes — switch to "Solve Missing Value" mode. Pick which row is unknown with its radio button, enter every other row's value and weight, type the target weighted average you want to hit, and the calculator works the formula backward to tell you what that last value needs to be.
What happens if I leave a row's value or weight blank?
A row needs both a value and a weight to be counted — if either box is empty, that row is skipped from the calculation without raising an error, the same way an empty row from clicking "Add row" one too many times is simply ignored. This lets you keep a few spare blank rows around for later without breaking the current result.
Can weights be zero, negative, or greater than 1?
Weights just need to be greater than zero — they don't have to add up to 1 or to any particular total, since the formula divides by the sum of the weights you actually enter. A weight of 0 or a negative weight isn't allowed because it would make that row cancel out or subtract from the average in a way the total-weight denominator can't sensibly absorb. Values, on the other hand, can be positive, negative, or zero.
Why doesn't my calculated GPA match my school's official transcript?
Registrars sometimes weight courses differently than a straight credit-hours model — some exclude pass/fail or withdrawn courses, some weight honors/AP courses on a different scale, and some average per-term GPAs together instead of recomputing from every individual course. This calculator does the plain, textbook weighted-average math; check your school's specific grading policy if the two numbers disagree.