How weighted average calculator works
A plain average treats every number as equally important, but real data rarely is. A 4-credit course should influence your GPA more than a 1-credit seminar; a 40% exam should count more than a 5% quiz. The weighted average fixes this by multiplying each value by its weight before dividing: sum every (value × weight) pair, then divide by the sum of the weights. When the weights happen to add up to 1 (like percentages totalling 100%), that division disappears and the weighted sum is the answer directly.
This tool takes two matching lists — the values and their weights — and returns the weighted average, the total weight, the weighted sum, and each item's share of the result. It also shows the unweighted mean beside it so you can see exactly how much the weighting moved the answer: if grades 85, 92, 78, 94 are weighted 0.25, 0.25, 0.20, 0.30, the weighted average is 88.05 while the plain mean is 87.25 — the strongest score pulled the result up because it carries the biggest weight.
Weights can be any non-negative numbers: percentages that sum to 100, credit hours, counts of observations, or raw importance scores — the tool divides by the total, so only the ratios between weights matter. A weight of zero effectively removes an item from the average while keeping it visible in the table. Common uses include course grades, blended hourly rates, portfolio returns weighted by position size, and averaging rates measured over different sample sizes.