How do you calculate a weighted average?

Multiply each value by its weight, add those products up, then divide by the total of the weights. Here that is (88 × 20) + (92 × 30) + (79 × 50) = 8470, and 8470 ÷ 100 = 84.7. The tool prints that line in full, plus a table showing what each pair contributed and what share of the total weight it carried.

How do I calculate my grade with weighted categories?

Put each category's score on a line with the percentage it is worth: homework 88 at 20, midterm 92 at 30, final 79 at 50. The weights do not have to be percentages and they do not have to reach 100. Only their proportions matter, so 3 and 1 weigh exactly as 75 and 25 do, and the tool says what your weights added up to so a missing category is visible.

Why is the weighted average lower than the plain average?

Because the heaviest weight sat on the lowest value. The 79 carries half the total weight on this page, so it pulls the answer down to 84.7 while the unweighted mean of the same three marks is about 86.3. Whenever the two disagree, the row table shows which pair is doing it: the largest contribution beside the largest share.

What if a weight is zero, or a line has only one number?

A zero weight is allowed and simply contributes nothing, which is what an ungraded category should do. A line that does not hold exactly two numbers is refused by name, with the line number and what it says, rather than being skipped quietly: a dropped row changes the answer without changing anything you can see. If every weight is zero there is no average to give, and the tool says that instead of dividing by nothing.

Can I get the mean, median and standard deviation too?

Yes. Switch What to work out back to All statistics and paste a plain list of numbers: mean, median, mode, range, both standard deviations, the geometric and harmonic means, each with its working. For letter grades and credit hours rather than numbers and weights, the GPA calculator does the same arithmetic with the grade scale built in.

Can I calculate a weighted percentage, a rating or a mean from frequencies?

Yes. Enter each percentage, rating or value with the number of observations it represents as its weight. For ratings 5 appearing once and 15 appearing three times, enter 5 1 and 15 3: the weighted mean is 12.5. For percentages 50 from a group of 10 and 100 from a group of 90, enter 50 10 and 100 90: the overall percentage is 95. This uses supplied exact values and frequencies, rather than grouped class intervals whose values are unknown.

How do I calculate a weighted average in Excel?

Put numeric values in A2:A4 and their weights in B2:B4, then use =SUMPRODUCT(A2:A4,B2:B4)/SUM(B2:B4). The weights need not add up to 100. Excel percentage cells use decimal values, so 20% is 0.2; use consistent units and format the result accordingly. This page calculates the same formula in the browser and does not generate a downloadable Excel workbook.

Can I average supplied share prices or unit costs?

For the average price per unit of known purchases, enter each purchase price as the value and the purchased quantity as its weight. Buying 10 shares at 100 and 20 at 80 gives (100 × 10 + 80 × 20) / 30, or about 86.666667 per share. The same arithmetic works for supplied crypto quantities or other units in one currency. Enter only amounts you know; the calculator does not fetch prices, reconstruct trades, calculate tax cost basis, allocate sales or recommend averaging down.

How do I average known rates or balances with different sizes or durations?

For a simple principal-weighted average of supplied rates, enter each rate with its corresponding principal as the weight. For a known time-weighted balance, enter each balance with the number of days it applied. The calculator averages those supplied pairs; it does not infer missing dates, effective borrowing costs, loan terms, tax rules or account interest. A geometric average of period returns uses growth factors instead of this arithmetic weighted mean.

Can I calculate a weighted atomic mass from supplied isotope data?

Enter each known isotope mass as the value and its supplied abundance as the weight, keeping abundances in the same convention. For hypothetical masses 10 and 12 with weights 75 and 25, the weighted mass is 10.5. This is the numeric weighted sum divided by total abundance; no isotope masses or natural abundances are looked up.

What happens when a raw weighted sum is too large or too small?

The mean can still be representable when a row product or raw sum is not. The calculator then uses normalized weight shares and labels unavailable intermediate figures Not representable. For 1e-300 and 2e-300 with equal weights of 1e-100, the weighted mean is 1.5e-300 even though their raw products cannot be held. Missing intermediate figures cannot be copied as numbers. If a normalized contribution cannot be represented reliably either, the message explains what to rescale.

Weighted Average Calculator

Every value with its own weight, one pair on each line, and the answer with both sums printed. This page opens on a gradebook: 88 at a weight of 20, 92 at 30 and 79 at 50, which is 8470 divided by a total weight of 100, so the weighted mean is 84.7. Averaging the three marks and forgetting the weights gives about 86.3, and that is a different grade.

Weighted mean · 3 values84.78470 ÷ 100 · total weight 100

What to work out

Value and weight, one pair a line: 88 20 92 30 79 50

Count: 3

One pair on each line: the value first, then the weight it carries, separated by a space, a comma or a tab. Weights need not add up to 100: only their proportions matter, so 3 and 1 weigh exactly as 75 and 25 do. A line that does not hold two numbers is named rather than skipped.

The workingvalue times weight, added up, over the total weight
(88 × 20) + (92 × 30) + (79 × 50) = 8470, and 8470 ÷ 100 = 84.7
Weighted meanthe answer
84.7
Sum of value times weightthe top of the division
8470
Total weightthe bottom of the division
100

Value	Weight	Share of the total weight	Value × weight
88	20	20%	1760
92	30	30%	2760
79	50	50%	3950

A weighted mean is not the mean of the values. Averaging the values and leaving the weights out answers a different question: for 88 at a weight of 20, 92 at 30 and 79 at 50, the plain mean is about 86.3 while the weighted mean is 84.7. Every row above shows what it put into the sum, so a component that is quietly deciding the answer can be seen doing it.

Common questions

How do you calculate a weighted average?: Multiply each value by its weight, add those products up, then divide by the total of the weights. Here that is (88 × 20) + (92 × 30) + (79 × 50) = 8470, and 8470 ÷ 100 = 84.7. The tool prints that line in full, plus a table showing what each pair contributed and what share of the total weight it carried.
How do I calculate my grade with weighted categories?: Put each category's score on a line with the percentage it is worth: homework 88 at 20, midterm 92 at 30, final 79 at 50. The weights do not have to be percentages and they do not have to reach 100. Only their proportions matter, so 3 and 1 weigh exactly as 75 and 25 do, and the tool says what your weights added up to so a missing category is visible.
Why is the weighted average lower than the plain average?: Because the heaviest weight sat on the lowest value. The 79 carries half the total weight on this page, so it pulls the answer down to 84.7 while the unweighted mean of the same three marks is about 86.3. Whenever the two disagree, the row table shows which pair is doing it: the largest contribution beside the largest share.
What if a weight is zero, or a line has only one number?: A zero weight is allowed and simply contributes nothing, which is what an ungraded category should do. A line that does not hold exactly two numbers is refused by name, with the line number and what it says, rather than being skipped quietly: a dropped row changes the answer without changing anything you can see. If every weight is zero there is no average to give, and the tool says that instead of dividing by nothing.
Can I get the mean, median and standard deviation too?: Yes. Switch What to work out back to All statistics and paste a plain list of numbers: mean, median, mode, range, both standard deviations, the geometric and harmonic means, each with its working. For letter grades and credit hours rather than numbers and weights, the GPA calculator does the same arithmetic with the grade scale built in.
Can I calculate a weighted percentage, a rating or a mean from frequencies?: Yes. Enter each percentage, rating or value with the number of observations it represents as its weight. For ratings 5 appearing once and 15 appearing three times, enter 5 1 and 15 3: the weighted mean is 12.5. For percentages 50 from a group of 10 and 100 from a group of 90, enter 50 10 and 100 90: the overall percentage is 95. This uses supplied exact values and frequencies, rather than grouped class intervals whose values are unknown.
How do I calculate a weighted average in Excel?: Put numeric values in A2:A4 and their weights in B2:B4, then use =SUMPRODUCT(A2:A4,B2:B4)/SUM(B2:B4). The weights need not add up to 100. Excel percentage cells use decimal values, so 20% is 0.2; use consistent units and format the result accordingly. This page calculates the same formula in the browser and does not generate a downloadable Excel workbook.
Can I average supplied share prices or unit costs?: For the average price per unit of known purchases, enter each purchase price as the value and the purchased quantity as its weight. Buying 10 shares at 100 and 20 at 80 gives (100 × 10 + 80 × 20) / 30, or about 86.666667 per share. The same arithmetic works for supplied crypto quantities or other units in one currency. Enter only amounts you know; the calculator does not fetch prices, reconstruct trades, calculate tax cost basis, allocate sales or recommend averaging down.
How do I average known rates or balances with different sizes or durations?: For a simple principal-weighted average of supplied rates, enter each rate with its corresponding principal as the weight. For a known time-weighted balance, enter each balance with the number of days it applied. The calculator averages those supplied pairs; it does not infer missing dates, effective borrowing costs, loan terms, tax rules or account interest. A geometric average of period returns uses growth factors instead of this arithmetic weighted mean.
Can I calculate a weighted atomic mass from supplied isotope data?: Enter each known isotope mass as the value and its supplied abundance as the weight, keeping abundances in the same convention. For hypothetical masses 10 and 12 with weights 75 and 25, the weighted mass is 10.5. This is the numeric weighted sum divided by total abundance; no isotope masses or natural abundances are looked up.
What happens when a raw weighted sum is too large or too small?: The mean can still be representable when a row product or raw sum is not. The calculator then uses normalized weight shares and labels unavailable intermediate figures Not representable. For 1e-300 and 2e-300 with equal weights of 1e-100, the weighted mean is 1.5e-300 even though their raw products cannot be held. Missing intermediate figures cannot be copied as numbers. If a normalized contribution cannot be represented reliably either, the message explains what to rescale.

Uses browser double precision with compensated sums and stable variance calculations. Median positions and mode frequencies are exact for the parsed numbers; arithmetic results can round. Unrepresentable inputs and intermediate results are explained.