How to Calculate Maximum EPI and PPI for a Fabric with Given Count

A Reader has asked me this question:

“ I want to know how to calculate max EPI and PPI of the given count. For Example, if we take 50s pv warp X 150 D  100% polyester weft, what will the max EPI and PPI if we weave it for plain, 2/2 twill,and satin.”

Here Mr. Ashenhurst can rescue us. The following method is based on his book “Textile Calculation and Structure of Fabrics”. Here the assumption is there is only one count of thread in both warp and weft. If there are two different counts of warp and wefts, threads per inch should be found out for both of them and then suitably adjusted.

The General formula to calculate Maximum EPI and PPI for a Given count of Warp and Weft

Now in a plain weave in a repeat there are 2 threads and 2 intersections. For 2/2 Twill in one repeat of 4 threads there will be 4 threads and 2 intersections.

Also as a rule please remember that 40s count yarn diameter is 1/165 of an inch.

To convert it to the yarn diameter of 50s warp we use the following formula

Which means for 50s PV Warp the diameter will be

Thus the Maximum Threads per inch for a plain weave will be 184 as this will be the diameter of the Yarn.

For 2/2 Twill be they will be ( From the Formula above)

Which means x will be equal to 122 threads per inch

Similarly for Satin weave one can find out the maximum ends and picks per inch

Please remember however that this is theoretical construct. Actual threads per inch are generally less than that.

To Calculate the Cotton Equivalent of 150 D, We use the formulaà count= 5315/denier, Which means it is equal to 35.43 or 35 count.

The Diameter for 35 count yarn will be ( Using the formula above) = 154.34 th of an inch

Then you can use the same equation to calculate the Maximum EPI and PPI

In these examples there is no allowance for bending, shrinkage or compression, the threads should be reduced or increased proportionately in case the fabric is subjected to bending, shrinkage or compression.