To know the performance of a garment factory and for the 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 ran 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 the above data you have to calculate the following using the above information 
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 ran 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 the above data you have to calculate the following using the above information 
a. Total minutes produced by the line:
To calculate 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:
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 operators worked in a line for 8 hours. They produced 160 garments and the SAM of the garment (style) 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 examples, refer to the following table. The 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?