Weighted Average Rate
Averaging two rates directly is wrong. Multiply each rate by its group size, add them, then divide by the total size.
Your numbers
Percentage
9.5%
Result
12.5%
What it means
The weighted 9.5% differs from the simple average of 12.5% — it leans toward the larger group.
Formula
Percentage = (A × A share + B × B share) ÷ (A + B)
A 20% defect rate on 300 units plus 5% on 700 gives 9.5% overall, not the 12.5% a simple average suggests.
What to enter
| Input | Default | Accepted range |
|---|---|---|
| AThe first number of the ratio — the 2 in 2:3. | 300 | 0 and up |
| A share (%)The percentage that applies to the first item. | 20 | 0 and up |
| BThe second number of the ratio — the 3 in 2:3. | 700 | 0 and up |
| B share (%)The percentage that applies to the second item. | 5 | 0 and up |
Step by step
Quick reference table
Results when only A changes and everything else stays put.
| A | Percentage (%) | Result (%) |
|---|---|---|
| 150 | 7.65 | 12.5 |
| 225 | 8.65 | 12.5 |
| 300 | 9.5 | 12.5 |
| 450 | 10.87 | 12.5 |
| 600 | 11.92 | 12.5 |
What each result means
| Result | At default values |
|---|---|
| Percentage (%)A share expressed out of 100. | 9.5 |
| Result (%)What the formula gives back — the answer this page is for. | 12.5 |
Common mistakes
A 20% defect rate on 300 units plus 5% on 700 gives 9.5% overall, not the 12.5% a simple average suggests.
Glossary
- A
- The first number of the ratio — the 2 in 2:3.
- A share
- The percentage that applies to the first item.
- B
- The second number of the ratio — the 3 in 2:3.
- B share
- The percentage that applies to the second item.
- Percentage
- A share expressed out of 100.
- Result
- What the formula gives back — the answer this page is for.
Frequently asked questions
Q. How is Weighted Average Rate calculated?
Percentage = (A × A share + B × B share) ÷ (A + B) — Averaging two rates directly is wrong. Multiply each rate by its group size, add them, then divide by the total size.
Q. Can you walk through an example?
With A 300, A share 20%, B 700, B share 5%, the answer is Percentage 9.5%.
Q. What do I need to enter?
Enter A, A share, B, B share. The result recalculates as you type, and an empty box counts as zero.
Q. How much does the answer move if I change a number?
Changing only A moves the answer to A 150 → Percentage (%) 7.65 and A 600 → Percentage (%) 11.92. The table below lays out five steps.
Q. How are the numbers rounded?
Money is shown to the nearest whole unit, percentages to one decimal place and everything else to two. What you see is rounded; the calculation itself carries the unrounded value forward.
Q. Anything to watch out for?
A 20% defect rate on 300 units plus 5% on 700 gives 9.5% overall, not the 12.5% a simple average suggests.
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