To determine thread consumption you just need to multiply seam length with those factors. This way one can estimate the total thread requirement for making a garment.


Actual thread consumption  for a unit length depend Varied:

The Following  Factor:


  1. Stitch Classes
  2. Stitches per inches (SPI)
  3. The thickness of the seam (fabric thickness)
  4.  Thread count 

Step 1: To calculate thread ratio, you need a sewing machine, fabric and sewing thread that will be used for bulk production. For fabric and thread, you can take similar thickness and same thread count in case actual is not available.    https://amzn.to/3myEOQ1

Step 2: Sew a seam of 15.5 cms long and take 10 cms seam out of it by trimming 1 cm from both edges.

Step 3: Unravel both needle thread and bobbin thread from the seam. measure its length in cm. Generally, it will be higher than the seam length. Now find the multiplying factor by dividing thread length with seam length. Assume needle thread length is 15.5 cm then needle thread multiplying factor is 15.5/10 or 1.55.
Using this method you can find out consumption factors.

Step 4:  Total thread consumption +Add thread wastage 5% for the thread that trims out from each end of the seam.