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Thread Formulas

While you typically won’t need to know these formulas, we think it is important that you understand the differences in different types of thread and how that affects yield and strength. Have a question about some of the terms used? We have a full list of thread terms to answer your most pressing questions.

Thread Yield

Yield refers to the yards per pound of product, using the following formula:

Equivalent Yarn Number (EYN) x 840 = Yield

** 840 is a constant in this equation. The formula to find EYN is explained below.

Here’s a handy quick reference for thread yield (consider it a cheat sheet).  These yields apply to both 100% polyester and poly/cotton blends. Below we will explain how the yield is determined.

As you can see from the below table, the greater the number of plies, the lower the yield; however, the greater the plies, the stronger the yarn.

Thread Type

Yield (yds/lb)

12/4 2520
12/5 2016
12/6 1680
13/4 2730
13/5 2184

How Much Thread Do You Need?

Pounds of thread needed = total yards / yield


This example will help you bring it all together:

Assume your bags are 36″ in width and you use 12/5 Poly/Cotton.  You need to know how much thread you will need to order to close 100,000 bags.

Lbs needed = total yards / yield

  • Determine how much thread you will need per bag.  This will typically be three times the width of your bag.
    • Using a 24″ bag to close
      • 24 x 3 = 72″ per bag
      • 72″/12″ = 6′ per bag
  • Convert total amount of thread needed per bag into yards.
    • 6’/3 = 2 yards of thread needed per bag
  • Calculate the total yards of thread you will need to complete your job.
    • 125,000 bags x 2 yards needed per bag = 250,000 total yards of thread needed
  • Determine yield using yield and EYN formula above (or use our handy chart above).
    • EYN = 12/5 Polyester
    • EYN = 2.4
    • Yield = EYN x 840
    • Yield = 2.4 x 840
    • Yield = 2016 yards per pound
  • Divide total yards of thread needed by thread yield to find total pounds of thread needed.
    • Pounds needed = 250,000 / 2016
    • Pounds needed = 124 pounds

Equivalent Yarn Number (EYN)

EYN represents plied yarn as if it were a singles yarn.

Yarn Count / Ply = EYN

Yarn Count or Yarn Number

The size or fineness of yarn. The number relates a unit length to a unit weight. Generally referred to as the number of 840 yard hanks per pound.

Example: 12.00’s yarn
= 12 hanks per pound
= 12 x 840 yards
= 10,080 yards per pound