Weighted Average Calculator

Real-world use cases

• Compute a syllabus grade from weighted components

  Your syllabus says homework 20 percent, midterm 30 percent, final 50 percent. Drop a row for each: your homework score with weight 20, midterm with 30, final with 50. The weighted average is your course grade, and the contribution column shows the final exam is doing half the work — so you know which score to fight for before finals week.

• Roll several class GPAs into one credit-weighted number

  Each course earns a grade point and carries credit hours. Put the grade point as the value and the credits as the weight, one row per class. The result is your GPA, weighted exactly the way a registrar computes it: a 4-credit A pulls harder than a 1-credit one. Share the link with an advisor and the whole transcript reopens as you entered it.

• Find a portfolio's blended return

  You hold three positions with different returns and different dollar amounts. Enter each return as the value and the amount invested as the weight. The weighted average is your money-weighted return, and the contribution share tells you which holding actually drove the number, not just which one had the flashiest percentage.

• Average customer ratings across uneven groups

  Three regions rate a product 4.5, 3.8 and 4.9, but they have 120, 64 and 210 respondents. A plain average of the three numbers overweights the small region. Use the respondent counts as weights and the weighted average reflects what your whole customer base actually thinks.

• Blend supplier prices by purchase volume

  You buy the same part from several suppliers at different unit prices and different quantities. Put the unit price as the value and the quantity as the weight to get your true blended cost per unit — the number that matters for a budget, not the simple average of the quotes.

Common pitfalls

• Taking a plain average of percentages that already carry different weights. Averaging a 70 percent component scoring 90 and a 30 percent component scoring 80 as (90+80)/2 = 85 is wrong; the weighted answer is 83. If the parts have different shares, you must weight them.

• Forcing weights to add up to 1 by hand and rounding along the way. There is no need — enter raw credits, dollars, or counts and let the tool divide by the real total. Pre-rounding 1/3 to 0.33 three times loses a point the formula would have kept.

• Pairing the wrong value with the wrong weight after reordering rows. Each row's weight must belong to the value on that same row. Use the contribution column as a sanity check, because if a row you expected to dominate shows a tiny share, a value and weight got crossed.

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