How to Calculate Weighted Average: A Step-by-Step Guide
Calculates averages where items count differently, like weighted exam components.
These calculations come up in school, at work and in daily life, from PSLE and O-Level practice to measuring a room for new flooring. Doing them by hand builds understanding, and a calculator lets you check the answer instantly.
What you need
- Values
- Weights
Step by step
- Enter the values.
- Enter the weights.
- The results update as you type, or press Calculate.
- Read the weighted average first, then the supporting figures below it.
The formula
Weighted mean = Σ(value × weight) ÷ Σweight.
Worked example
For example, with these inputs:
- Values: 80, 72, 90
- Weights: 30, 30, 40
the calculator returns:
- Weighted average: 81.6
Practical tips
- When numbers are very large or small, scientific notation makes them easier to compare.
- Keep units consistent: convert everything to the same unit before calculating.
- Estimate the answer roughly first so you can spot a result that is clearly wrong.
- Check your answer by working backwards from the result.
Background
Rounding is a common source of small errors. Keep full precision during intermediate steps and round only the final answer to the number of decimal places or significant figures the question asks for.
A quick mental estimate before calculating is a powerful check. If a room's floor area comes out at 4,000 square metres or a percentage comes out above 100% when it should not, you know to look again.
These calculations appear throughout the Singapore syllabus, from primary school percentages and fractions to secondary school algebra and geometry. Understanding the formula makes problem sums easier because you can recognise which quantity is missing.
Related calculations
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- Area of an Ellipse Calculator: Calculates the area of an ellipse from the measurements you enter.
- Area of a Rhombus Calculator: Calculates the area of a rhombus from the measurements you enter.
Want to skip the arithmetic? The free Weighted Average Calculator does all of this instantly and updates as you type.
Run your own numbers: Weighted Average Calculator