To know the performance of a garment factory, and a comparative study of the sewing line performance, we measure production line efficiency. So, like individual operator efficiency, measuring the efficiency of a production line is important for a factory. Daily line efficiency shows line performance.
1. Number of operators – how many operators worked in the line in a day
2. Working hours (Regular and overtime hours) – how many hours each of the operators worked or how many hours the line run in a day
3. Production in pieces – How many pieces are produced or total line output at the end of the day
4. Garment SAM – What is the exact standard minute of the style (garment)
Once you have above data you have to calculate following using above information 
a. Total minutes produced by the line: To get total produced minutes, multiply production pieces by garment SAM
b. Total minutes attended by all operators in the line: Multiply the number of operators by daily working hours and convert total hours into total minutes (multiplying by 60).
Now, calculate line efficiency using the following formula:
48 operations worked in a line for 8 hours. They produced 160 garments and SAM of the garment is 44.25 minutes.
Here,
Total minutes produced = (160 x 44.25) = 7080 minutes
Total minutes attended = (48 operator x 8 hours x 60) = 23040 minutes
Effiicnecy% = (7080 x100)/23040 % = 30.729%
For more example, refer to the following table. Data calculation formula has been given on the header row of the table.
Production Line Efficiency Calculation  Information required
To calculate the efficiency of a line for a day, you will need the following data (information) from the line supervisor or line recorder.1. Number of operators – how many operators worked in the line in a day
2. Working hours (Regular and overtime hours) – how many hours each of the operators worked or how many hours the line run in a day
3. Production in pieces – How many pieces are produced or total line output at the end of the day
4. Garment SAM – What is the exact standard minute of the style (garment)
Once you have above data you have to calculate following using above information 
a. Total minutes produced by the line: To get total produced minutes, multiply production pieces by garment SAM
b. Total minutes attended by all operators in the line: Multiply the number of operators by daily working hours and convert total hours into total minutes (multiplying by 60).
Now, calculate line efficiency using the following formula:
Line efficiency (in percentage) = (Total minutes produced by the line *100) /(Total minutes attended by all operators)
An Example  Calculating Production Line Efficiency
Let's calculate the line efficiency of one production line.48 operations worked in a line for 8 hours. They produced 160 garments and SAM of the garment is 44.25 minutes.
Here,
Total minutes produced = (160 x 44.25) = 7080 minutes
Total minutes attended = (48 operator x 8 hours x 60) = 23040 minutes
Effiicnecy% = (7080 x100)/23040 % = 30.729%
For more example, refer to the following table. Data calculation formula has been given on the header row of the table.
No. of
Operator (A) 
Working
hours (B) 
line output
(production) (C) 
Garment
SAM (D) 
Total
minutes
attended (E=A*B*60) 
Total Minute
produced (F=C*D) 
Line
Efficiency (%) (F/E*100) 
48

8

160

44.25

23040

7080

30.73

48

11

240

44.25

31680

10620

33.52

34

8

300

25

16320

7500

45.96

35

11

400

25

23100

10000

43.29

35

11

329

25

23100

8225

35.61

34

8

230

25

16320

5750

35.23

34

8

200

35

16320

7000

42.89

35

11

311

35

23100

10885

47.12

34

11

340

35

22440

11900

53.03

Here is one Video Guide for calculating overall efficiency.
Related Topics:
How to calculate SAM for a garment?
Garment CM cost estimation using SAM or SMV
The Concept of Operator's Performance Rating
How to calculate operator efficiency at work?
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