Line efficiency tells you how much of the time a sewing line had was turned into standard work. It is the most watched number in garment production, and one of the most misused.
The formula#
- Output is good garments completed in the period.
- SMV is the standard minute value of the garment.
- Manpower is the number of people counted in the line.
- Working minutes is the time each person was available in the period.
The top of the fraction is earned minutes: the standard time for the work done. The bottom is available minutes: the time paid for. Efficiency is the ratio.
Worked example#
A T-shirt line has 40 people and works 8 hours (480 minutes). The garment SMV is 12.0. At the end of the day, 1,000 good T-shirts have passed end-of-line checking.
- Earned minutes = 1,000 × 12.0 = 12,000
- Available minutes = 40 × 480 = 19,200
- Efficiency = 12,000 / 19,200 × 100 = 62.5%
Try your own numbers in the line efficiency calculator.
What efficiency really measures#
Efficiency above 100% means the line earned more standard minutes than it had. That can be genuine on a mature style with skilled operators, but it more often means the SMV is too loose, output was over-counted or manpower was under-counted.
Efficiency well below plan means time was lost somewhere. The loss usually comes from a combination of:
| Source of loss | Examples |
|---|---|
| Balancing | Operators waiting for work behind a bottleneck |
| Method | Poor workplace layout, missing attachments, extra handling |
| Skill | New operators, operators on unfamiliar operations |
| Machines | Breakdowns, wrong settings, needle and thread problems |
| Material | Late cut panels, missing trims, shade or measurement problems |
| Quality | Time spent on repairs instead of new work |
| Style changes | Learning curve after a changeover |
The low line efficiency troubleshooting guide works through these in order.
Off-standard time#
Some lost minutes are outside the line's control: a power cut, waiting for cut panels, a machine waiting for a mechanic. Many factories record these minutes as off-standard time and calculate two numbers:
On-standard efficiency shows how well the line worked when it could work. Overall efficiency shows the business result. Both are useful; report which one you are using.
Who counts as manpower#
This is the most common source of disagreement. Decide once, write it in your procedure, and keep it:
- Operators only gives a higher number, useful for comparing operator performance.
- Operators and helpers reflects the direct labour cost of the line.
- All line staff, including supervisors, line quality checkers and ironmen, reflects the full cost.
A line's efficiency can move by ten points just from a change in who is counted. That tells you nothing about how the line worked.
Efficiency and targets#
Target and efficiency are the same equation rearranged:
A line planned at 65% with 40 people, 480 minutes and SMV 12 has a daily target of 1,040 pieces. If it makes 1,000, it ran at 62.5%. See production target calculation.
Improving efficiency#
Work on causes, not on the number:
- Balance the line so no operator waits and none is overloaded. See line balancing and bottleneck analysis.
- Fix the method at the slowest operations: workplace layout, attachments, folders, pick-up and aside positions.
- Keep machines ready: correct needles, tension, SPI and preventive maintenance.
- Secure material flow from cutting so the line never waits for input.
- Build quality in with inline checks, so time is not lost on repairs.
- Plan for the learning curve when styles change.
Common reporting mistakes#
- Counting repaired or unchecked garments as output.
- Using a costing SMV that is different from the SMV the line is working to.
- Mixing overtime minutes in or out between days.
- Changing the manpower definition between lines or reports.
- Comparing efficiency between factories without checking SMV method and scope.
Related measures#
- Operator efficiency applies the same idea to one person and one operation.
- Pieces per operator per day is simpler but meaningless across different styles.
- OEE is used for machine-paced processes. See OEE in garment manufacturing.
The capacity calculator uses average efficiency to plan how much a factory can book.