When to use a weighted average
A simple average treats every value equally. A weighted average lets some values count more than others — which is what you want when the items aren't equally important. Course grades where each assessment carries a different percentage, a portfolio where holdings differ in size, or product ratings with different numbers of reviews are all classic cases.
How it's calculated
Each value is multiplied by its weight, those products are added together, and the total is divided by the sum of the weights. The weights don't need to add up to 100 — any consistent scale works, because dividing by their total normalises them.
Frequently asked questions
Do the weights have to add up to 100?
No. Weights can be percentages, credit hours, share counts or anything consistent — the calculator divides by their total, so the scale cancels out.
What if my two lists are different lengths?
The calculator will tell you, because every value needs a matching weight. Trim whichever list is longer so they pair up.
Can weights be decimals?
Yes. Values and weights can both be decimals; negative weights are allowed but unusual.