Your data
Paste a table straight from Excel or Google Sheets, or drop a CSV file. Nothing is uploaded anywhere — the whole calculation runs inside this browser tab.
CSV, TSV or plain text. Files saved in windows-1251 are detected and re-read automatically, so Cyrillic headers do not turn into garbage.
Parsing options
Columns
Result
Save and share
The drawing library is downloaded only when you press the button, and only on this page.
This page has no server side at all. The table you paste is parsed by JavaScript inside your own browser, the chart is drawn on a canvas element on your machine, and the export file is assembled locally. Nothing is uploaded, stored or written to any log. You can disconnect from the network after the page has loaded and everything will still work — which is the simplest way to verify the claim yourself.
Facts and limits of this method
| Formula | Σ(value × weight) ÷ Σ(weight) |
|---|---|
| Also shown | The plain arithmetic mean, for comparison |
| Contribution | Each row exported with its share of the final result |
| Equal weights | The weighted mean collapses to the plain mean exactly |
| Zero total weight | Undefined; the tool reports it instead of dividing by zero |
| Negative weights | Permitted arithmetically but almost always a data error |
When it misleads you
- The gap between the weighted and the plain mean is the measure of how much a few heavy rows are driving the result. When it is large, reporting the weighted figure alone hides that a handful of rows produced it.
- Weights must be on a meaningful scale. Doubling every weight leaves the result unchanged, but replacing credits with an arbitrary importance score changes it entirely — and there is no way to check whether that score was defensible.
- A single dominant weight makes the average almost meaningless. If one row carries 90% of the total weight, the weighted mean is essentially that row’s value with a small correction.
- Negative weights are computable and produce results that violate every intuition about averages: the answer can fall outside the range of your values entirely. If they appear, they are almost certainly a mistake in the data.
How it is calculated
Each value is multiplied by its weight, the products are summed, and the total is divided by the sum of the weights. Dividing by the weight total is what keeps the result on the same scale as the original values rather than growing with the size of the weights.
The plain arithmetic mean is computed alongside and displayed next to it. The comparison is the useful part: identical values mean the weighting changed nothing, and a large gap means a few heavily weighted rows are carrying the result.
Every row is exported with its contribution — its value times its weight, divided by the total weight. Those contributions sum to the weighted mean, which makes it possible to see exactly which rows produced the answer instead of taking the single number on trust.
When the weights sum to zero the calculation is undefined, and the tool says so rather than returning infinity. That happens with negative weights or an all-zero weight column, both of which are usually data errors worth investigating.
Questions and answers
When do I need a weighted average?
Whenever your rows represent different amounts of something: courses with different credits, prices across warehouses with different stock, survey responses from groups of different sizes.
Why is my weighted average identical to the plain one?
Because your weights are all equal, or nearly so. In that case weighting adds nothing, and the plain average is the simpler thing to report.
Can weights be percentages?
Yes. Any consistent scale works, because the formula divides by the total weight. Percentages, counts and credits all give the same answer if they are proportional to each other.
What if some rows have no weight?
Rows missing either the value or the weight are skipped as a pair and counted. A missing weight is not treated as zero, because a zero weight would silently exclude a row that may simply not have been measured.
Is my data uploaded?
No. Both averages and every contribution are computed in your browser.