Scrap rate is the quality number most shops already track, because scrap is visible: it ends up in a bin. The catch is everything it doesn’t count.
The scrap rate formula
Scrap rate = Scrapped or rejected quantity ÷ Total quantity produced × 100%. Both counts should cover the same part and the same period — a shift, a batch or a week — and the rule for what counts as scrap should stay the same from run to run.
A worked example
One batch on one machine (illustrative numbers):
Total parts produced
- Value
- 1,200
Scrapped
- Value
- 18
Reworked and shipped
- Value
- 42
| Input | Value |
|---|---|
| Total parts produced | 1,200 |
| Scrapped | 18 |
| Reworked and shipped | 42 |
Scrap rate = 18 ÷ 1,200 = 1.5%. Check your own batch in the scrap rate calculator.
Scrap rate vs rework vs FPY
The 42 reworked parts above don’t appear in the 1.5% at all. Counting them, first pass yield is (1,200 − 18 − 42) ÷ 1,200 = 95.0% — a much bigger quality problem than the scrap rate alone suggests.
That is why scrap rate works best next to FPY rather than on its own: scrap rate shows material thrown away, FPY shows how much time went into parts that needed a second attempt.