Weighted Average — When Not All Values Are Created Equal
A weighted average accounts for the fact that different data points contribute unequally to a final result. Unlike a simple average that gives every value the same importance, a weighted average multiplies each value by a weight factor that reflects its relative significance, then divides the total by the sum of all weights. The formula is: Σ(value × weight) / Σ(weight).
Common uses for weighted average calculations:
1. GPA calculation — Enter grade points as values and credit hours as weights. A 3-credit course has three times the impact on GPA as a 1-credit course.
2. Stock average cost basis — When buying shares at different prices, use shares purchased as the weight to find the true average cost per share.
3. Graded assessments — A course where exams count 60% and homework 40% requires a weighted average to compute the final grade correctly.
4. Survey data analysis — Likert scale responses (1–5) weighted by the number of respondents choosing each option produce an accurate mean rating.
5. Portfolio return — Weight each asset's return by its proportion of the total portfolio to calculate the overall weighted return.
6. Production quality — Compute a weighted defect rate across batches of different sizes.
The weights do not need to sum to any specific value. Whether you enter credit hours, percentages, raw counts, or arbitrary numbers, the calculator normalizes them automatically by dividing by the sum of all weights.
Frequently Asked Questions
A: Yes. Weights like 0.4, 0.6 (for 40%/60%) work just as well as 40 and 60. Any consistent scale produces the correct result.
A: They contribute equally to the average. Equal weights produce the same result as a simple average.
A: Yes, click the "Add Item" button to add as many rows as you need.