“The line ran at eighty per cent today.” Everyone on the floor nods. But eighty
per cent of what, measured how, with which people counted? The percentage is easy
to produce and very easy to get wrong, and a line manager who trusts a wrong one will spend
months fixing the wrong thing.
What the number actually is
Line efficiency compares two quantities of time:
- Minutes available — operators × hours worked × 60.
- Minutes earned — garments produced × SAM, the standard
minutes it should take to make one garment.
Efficiency is minutes earned divided by minutes available. It says how much of the paid
machine time was turned into finished work at the standard rate.
A worked example
These figures are made up to show the sum. They are not a benchmark and not a claim about
any line. They are the values the
production efficiency calculator opens with, so you can check them
there.
- 12 operators, 8 hours each
- SAM: 18 minutes per garment
- 260 good garments produced
Available: 12 × 8 × 60 = 5,760 minutes. Earned:
260 × 18 = 4,680 minutes. Efficiency: 4,680 ÷ 5,760 =
81.3%.
At 100% the same line would have made 5,760 ÷ 18 = 320 garments, so it was
60 short. The 1,080 minutes that were not earned are 18 hours of paid
machine time — two and a quarter operators' full days. That is the figure worth
taking to the floor: not “eighty-one per cent” but “eighteen hours of
sewing we paid for and did not get.”
Four ways the percentage goes wrong
1. A SAM nobody measured
Everything above depends on the 18. If it came from a buyer's sheet, a catalogue or a guess,
the efficiency is only as good as that number. Same line, same 260 garments, only the SAM
changes:
- SAM 15: 3,900 minutes earned, 67.7%.
- SAM 18: 4,680 minutes earned, 81.3%.
- SAM 21: 5,460 minutes earned, 94.8%.
Twenty-seven points between the lowest and the highest, with not one garment more or fewer
sewn. A figure above 100% almost always means the SAM is too generous, not that the line
beat the standard.
2. Counting rejects as produced
Only good pieces count. If those 260 garments include 15 that have to be redone, the good
ones are 245: 245 × 18 = 4,410 minutes earned, and efficiency is 76.6%.
Counting the rejects flattered the line by almost five points.
3. Counting the wrong people
Operators means people who sew. Helpers, checkers and the supervisor should be left out
unless they are on a machine. Count two helpers as operators and the available time becomes
14 × 8 × 60 = 6,720 minutes, so the same output reads
69.6%. The line did not get worse; the denominator got bigger.
4. Counting hours nobody sewed
Use paid hours actually on the machine. If the eight hours include an unpaid half hour for
tea, the real figure is 7.5 hours: 12 × 7.5 × 60 = 5,400 minutes, and the same
output is 86.7%.
Write down the rules once
Who counts as an operator, which hours count, whether rejects count, where the SAM came
from. Then use the same rules every day. A lower number measured the same way is more
useful than a higher number measured differently each time.
What the number cannot tell you
Efficiency says how much was lost. It does not say why. Machine
breakdowns, waiting for cut parts and style changeovers all appear as the same missing
minutes, and they have different fixes: a mechanic, the cutting room, the planning desk.
So when you find the missing minutes, do not stop at the percentage. For one week, have
each line supervisor write down every stoppage and what caused it, even roughly. At the end
of the week there is a short list, and the biggest item on it is where to start. You may
find that the line is losing more waiting for cut parts than to anything on the machines
— in which case the answer is in the cutting room, not on the sewing floor.
Why it reaches the price
The day's wages do not change when output falls. At 260 garments each one carries
one 260th of them; at 320, one 320th — 18.75% less labour on every
garment. Efficiency is therefore part of what a garment really costs, and the
costing sheet that prices it will be
wrong if its stitching cost was worked out on a good day.
What these sums leave out
- Output is not the only measure. A line can hit its efficiency by making
garments that fail inspection later; that is why rejects are taken out above.
- One day proves little. A new style, a power cut or a short fabric
delivery can move a single day by ten points. Look at a week.
- There is no number to aim at. Another unit's percentage, measured with
its own SAM and its own rules, tells you nothing about yours. Compare a line with
itself, week on week.
Put your own figures into the calculator; it shows the minutes
available, the minutes earned, the output at 100% and the shortfall, so the percentage is
never the only thing on the screen. If the missing minutes turn out to be in the cutting
room, the cutting wastage article is the
next place to look.