Weighted Average Calculator

A weighted average, also called a weighted mean, combines values while allowing some observations to contribute more than others. An ordinary arithmetic mean gives every value equal influence. A weighted mean instead multiplies each value by an associated weight, adds those products, and divides by the sum of all weights. This approach is appropriate whenever observations differ in importance, frequency, quantity, confidence, or share. The formula is the sum of each value times its weight divided by the sum of the weights. Weights do not have to add to 100. Percentages such as 30, 30, and 40 work, but proportional weights such as 3, 3, and 4 produce the same answer because both numerator and denominator scale together. The only requirement is that the total weight be greater than zero. This calculator accepts zero weights, which effectively exclude their associated values, but rejects negative weights because they are not meaningful for the common averaging use cases covered here. Grades are a familiar example. If exams account for 40 percent of a course while homework and projects have smaller shares, averaging all scores equally would misrepresent the grading policy. Investment returns provide another example: a return on a large holding should influence total portfolio performance more than the same return on a small holding. Product ratings can use response counts as weights, and mixture concentrations can use volumes or masses. Values and weights can use decimals. Values may also be negative, as with investment losses or temperatures, while weights remain nonnegative. Keep the meaning of weights consistent within one calculation. Do not mix percentages, counts, and monetary amounts unless they have first been converted to a common weighting basis. The weighted result uses the same conceptual unit as the values; the weights determine influence but do not change the value unit. A weighted average is not always the right summary. It can hide variation, outliers, or distinct groups just as an ordinary mean can. It also depends heavily on choosing defensible weights. When weights are estimated or subjective, report that uncertainty alongside the result. For statistical frequency data, verify whether you need a population mean, a sample estimate, or another estimator with specialized corrections. This calculator evaluates every complete value-weight pair and ignores rows where both entries are blank. Partially completed rows are not used, so complete each intended pair before calculating. The displayed total weight helps confirm that the inputs match your plan. Retain appropriate precision during calculation and round the final weighted mean according to the accuracy of the source values.