Weighted Average Calculator

ValueWeight

84.9

Weighted average

100

Σ weights

8,490

Σ (value × weight)

Rows counted

What a weighted average actually does

A regular average treats every value equally. A weighted average lets some values matter more than others. The formula: weighted average = Σ(value × weight) ÷ Σ(weight). Multiply each value by its weight, add the products, divide by the sum of the weights. That is the whole calculation — there is nothing else to it.

Excel has a function for this — SUMPRODUCT(values, weights) / SUM(weights) — but you need Excel. This page does the same thing in a browser tab, with no install and no subscription.

Worked example — class grade

A course has three components: homework (30% of the grade, score 85), midterm (40%, score 90), final (30%, score 78). Weighted average = (85 × 30 + 90 × 40 + 78 × 30) ÷ (30 + 40 + 30) = (2550 + 3600 + 2340) ÷ 100 = 8490 ÷ 100 = 84.9.

When weighted averages are the right tool

Grades — homework, midterm, final each carry a different percentage of the course.
Portfolio returns — each holding contributes a return weighted by the dollars invested in it.
Survey results — responses weighted by sample size, region, or demographic.
Inventory cost — weighted average cost of goods sold (WAC) when units were purchased at different prices.
Quality scores — composite scores where some metrics matter more than others.

Weighted vs. plain average

If every weight is the same, the weighted average equals the plain average. So a plain mean is just a weighted average with all weights set to 1. The difference matters the moment one input deserves to count more than another — and most of the time, in real numbers, one does.

A weighted average lets some values matter more than others. Each value is multiplied by its weight, the products are summed, then divided by the sum of the weights: Σ(value × weight) ÷ Σ(weight). Use it when inputs are not interchangeable — a course's midterm is worth more than a quiz, a $50,000 holding pulls more than a $500 one, a sample of 1,000 responses outweighs a sample of 10. If every weight is equal, the weighted average collapses to the plain average. Weight units do not matter — percentages, dollars, hours, headcounts all work, as long as you use the same unit down the column.

Built by Bob QA by Ben Shipped May 13, 2026

How to use

1
Type a value in the first column and its weight in the second. Weights can be percentages, dollars, hours — any consistent unit.
2
Press Enter on the last weight, or click Add row, to add another pair. There is no upper limit.
3
The weighted average updates as you type. Σ weights, Σ (value × weight), and the row count are shown alongside.
4
Tap Show full precision to expose the unrounded result; tap again to return to a clean 4-significant-digit display.
5
Empty rows are ignored, so you can leave gaps. Clear all resets to three blank rows.

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Frequently asked questions

What is the formula for a weighted average?

Weighted average = Σ(value × weight) ÷ Σ(weight). Multiply each value by its weight, add up all the products, then divide by the sum of the weights. That is the whole calculation — there are no other steps.

How is this different from a plain average?

A plain average (the arithmetic mean) treats every value equally. A weighted average lets some values count more than others. Mathematically, a plain mean is just a weighted average with every weight set to 1 — so the plain mean is a special case, not a separate idea. Use the plain version when inputs are interchangeable; use the weighted version when they're not.

Do the weights have to add up to 1 or 100?

No. The formula divides by the sum of the weights, so the totals scale automatically. Weights of 30, 40, 30 give the same answer as 0.3, 0.4, 0.3 or 3, 4, 3. Use whatever units make the problem clear — percentages for grades, dollars for portfolios, hours for time-weighted scores.

Can I use negative numbers?

Negative values are fine — they're common when averaging returns, adjusted scores, or signed differences. Negative weights are mathematically valid but almost always a typo; the calculator flags them with a warning so you can double-check before trusting the result.

What happens if all the weights are zero?

The math breaks — you would be dividing by zero. The calculator catches this and asks you to add at least one row with a non-zero weight. A single row with weight zero contributes nothing, so its value is effectively unused.

Why is the result rounded? Can I see the full number?

Most weighted averages don't need more than 4 significant digits to be useful — 84.9 reads cleaner than 84.90000000000001 (a floating-point artifact). Tap Show full precision to expose the unrounded value if you need every digit, for instance when feeding the result into another calculation.

Can I do this in Excel instead?

Yes — Excel has SUMPRODUCT. The formula is =SUMPRODUCT(values, weights) / SUM(weights). The catch is that you need Excel installed and a spreadsheet open. This page does the same calculation in a browser tab, with no install, no subscription, and no spreadsheet to set up.

Is my data saved anywhere?

No. The calculation runs entirely in your browser. Nothing is uploaded, stored, or sent to a server.

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