Weighted Average Calculator
Calculate a weighted average from a list of values and their corresponding weights — useful for grades, scores, and portfolios.
Why weighted average differs from a simple average
A simple average treats every value equally, but a weighted average lets some values count more than others — this matters whenever different items genuinely carry different importance, like a final exam worth more than a weekly quiz, or a large purchase mattering more to a portfolio's overall price than a small one.
Weights don't need to sum to exactly 1 or 100% for this calculator to work — since the formula divides by the total weight, proportional weights (like 2, 3, 2, 3) produce the same result as their equivalent percentages (20%, 30%, 20%, 30%).
Common uses for weighted averages
Weighted averages show up constantly: calculating a course grade from assignments worth different percentages, computing the average cost basis of shares bought at different prices and quantities, blending survey results where responses come from different-sized groups, and averaging investment returns weighted by amount invested.
Getting the weights right is the most important part of this calculation — an incorrect weighting scheme (like accidentally treating all items as equal) is one of the most common sources of error when calculating grades or blended scores by hand.
Frequently asked questions
Do my weights need to add up to 100%?
No — this calculator normalizes automatically by dividing by the total weight, so proportional weights (like 2, 3, 5) work the same as their percentage equivalents.
What happens if I enter a different number of values and weights?
The calculator uses only as many pairs as match up (the shorter of the two lists), so make sure your values and weights lists have the same number of entries, in the same order, for an accurate result.