Math & Statistics

Weighted Average Calculator

Calculates a weighted mean and shows what each row contributed, next to the unweighted mean.

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How to use this tool

  1. Put the value and its weight on one line, separated by a comma or a tab.
  2. Select Calculate.
  3. Check the total weight in the last row against what you expected — a missing line shows up there first.
  4. Compare the weighted figure with the unweighted mean shown in the summary to see what the weighting actually did.

What weighted average does

A weighted average is easy to compute and easy to get wrong, usually by dividing by the number of rows rather than by the total weight. This page divides by the weight, shows the total it used, and prints the plain unweighted mean beside it — so the gap between the two is visible, and that gap is the entire reason for weighting anything in the first place.

Every row shows its share of the total weight and how much of the final figure came from it, which is how you find the one line that is doing most of the work. Negative weights are accepted, because occasionally they are meant, but they are flagged in the summary because far more often they are a typo.

Frequently asked questions

The sum of the weights, not the number of rows. That total is printed in the last row so you can check it. Dividing by the row count instead is the single most common way a weighted average comes out wrong.

No. Any positive numbers work — counts, hours, credits, populations — because only the ratios between them matter. The share column converts them to percentages for you so you can see how the influence is distributed.

A zero weight simply removes that row from the result, which is a legitimate way to exclude a value. Negative weights are accepted but flagged, because they make the result hard to interpret and are far more often a typo or a sign error than a deliberate choice.