A weighted average gives some numbers more influence than others, instead of treating every value equally.
Why plain averages fall short
A plain arithmetic average treats every number the same. But in real life, some numbers should count more than others — such as a final exam worth 40% of your grade versus a quick pop quiz worth 5%, or a primary supplier that ships 70% of your inventory.
When relative importance differs across items, an unweighted mean gives a skewed, unrepresentative result. That is exactly where a weighted average comes in.
The weighted average formula
Multiply each value by its corresponding weight, sum all those weighted products together, and then divide by the total sum of all weights.
Weighted Average = Σ(value × weight) ÷ Σ(weights)
A worked step-by-step example
Imagine your university course grade is calculated from three components:
• Homework: score 85 (weight: 30% or 0.30)
• Midterm Exam: score 78 (weight: 30% or 0.30)
• Final Exam: score 92 (weight: 40% or 0.40)
Step 1: Multiply each score by its weight:
(85 × 0.30) + (78 × 0.30) + (92 × 0.40) = 25.5 + 23.4 + 36.8 = 85.7
Step 2: Divide by the sum of weights (0.30 + 0.30 + 0.40 = 1.0):
85.7 ÷ 1.0 = 85.7 final weighted score. Notice that a plain average would have been (85 + 78 + 92) ÷ 3 = 85.0. The weighted average properly credits the student for their strong final exam performance.
When to use a weighted average
Use a weighted average whenever data points hold unequal significance: calculating GPA, balancing an investment portfolio, blending survey results from customer cohorts of different sizes, or tracking supplier lead times.
Try the calculator
Open the Weighted Average Calculator to check your own values and weights.