Updated · Built and checked by the PlinzoTools team, formulas tested against published sources
Calculate a weighted average from a list of values and their corresponding weights.
This tool calculates a weighted average -- each value multiplied by its weight, summed, then divided by the total weight -- useful for grades weighted by credit hours, portfolio returns weighted by investment size, or any scenario where not every data point counts equally.
Enter up to four Value and Weight pairs in the separate fields provided (Value 1/Weight 1 and Value 2/Weight 2 are required; rows 3 and 4 are optional). The weighted average appears instantly.
The calculator provides four rows, each with a Value field and a Weight field. Rows 1 and 2 are the main ones and rows 3 and 4 are optional. There is no comma-separated value:weight box; you type each number into its own field. Any row whose weight is zero or blank is ignored completely, so leaving the optional rows empty simply means you are averaging two items. If the total of all usable weights is zero, the tool has nothing to divide by and shows a dash instead of a number. The result is displayed rounded to two decimal places.
Weighted average = (value1 × weight1 + value2 × weight2 + ...) ÷ (weight1 + weight2 + ...)
Suppose a course has three graded components with hypothetical scores. The homework score is 92 and counts for 2 units of weight, the midterm score is 78 and counts for 3 units, and the final exam score is 85 and counts for 5 units. Enter 92 and 2 in row 1, 78 and 3 in row 2, 85 and 5 in row 3.
Notice that the simple average of 92, 78 and 85 is 85.00. The weighted result is lower because the weakest score, the midterm, carries more weight than the strongest score, the homework.
A common worry is that weights must be percentages summing to 100. They do not. Because the formula divides by the total weight, you can use credit hours, dollars invested, number of items, or percentages, and the answer is the same as long as the proportions between weights are the same. Weights of 2, 3 and 5 give exactly the same result as 20, 30 and 50, or 0.2, 0.3 and 0.5. This makes it easy to enter whatever numbers your syllabus, portfolio statement or price list already shows.
A weighted average always falls between the lowest and highest value you entered. If it does not, something was typed incorrectly. It sits closer to the values with larger weights. Comparing it with the simple average is a quick way to see which items are pulling the result up or down. For a "what do I need on the final" question, run the calculator with a few different hypothetical final-exam scores and watch how the result moves.
For official grade calculations, always follow the method stated by your school or instructor, since some use different rounding or dropped-score rules.
The result becomes identical to a simple average -- weighting only matters when weights actually differ.
No. The tool divides by the total of whatever weights you enter, so only the proportions between them matter. Weights of 1, 2 and 3 behave the same as 10, 20 and 30.
Rows with a weight of zero or an empty weight field are skipped. Enter a positive weight for the row to be counted.
The calculator has four value and weight rows. For more items, group entries that share the same weight and enter their combined value with the combined weight.
The formula itself works with negative values, such as gains and losses, but the weights should be positive since rows with zero or negative weight are dropped.
Reference: NIST Weights and Measures