How Fabric Weight Is Built From Yarn Count, EPI and PPI

Why a buyer can work this out

A spec sheet gives you a construction line and a GSM, and they are not independent. A cloth cannot weigh whatever the seller says: its weight is fixed by how much yarn is packed into each square metre. That means a quoted GSM can be checked against the construction beside it in a few seconds. If the two disagree by a wide margin, one of them is wrong.

Our guides on yarn counts and blends and EPI and PPI explain what each number means. This one puts them together.

The formula

For a plain woven cloth in the cotton (Ne) count system, where the warp and weft counts are the same, the approximate weight before allowing for crimp is:

GSM ≈ 23.25 × (EPI + PPI) ÷ Ne

The number 23.25 comes from the Ne system itself: a yarn of count Ne has a linear density of 590.5 divided by Ne in tex, and an inch is 25.4 millimetres. You do not need to rework it, only to use it. If the warp and weft counts differ, work out each direction on its own and add them.

Crimp is the extra length of yarn that a thread uses because it goes over and under its neighbours rather than lying straight. It adds weight the bare formula does not count. A reasonable working allowance is 5 to 8 percent, but it varies with the weave and the tension, so treat the result as a range.

A worked example

Take a shirting with a construction of 40s by 40s, 80 ends by 72 picks, at 47 inches wide. Add the EPI and PPI to get 152, multiply by 23.25 to get 3,534 and divide by 40. That gives about 88 GSM before crimp.

Allowing 5 to 8 percent for crimp puts the weight at roughly 93 to 95 GSM. If a quote for this construction claims 120 GSM, something does not fit: either the count is coarser than stated, the thread density is higher, or the weight includes a heavy finish. If it claims 80 GSM, the cloth is lighter than the construction allows. Either way the quote needs an explanation.

Why the answer is approximate

Treat the result as a cross-check, not a specification. Several things move the real figure away from it. Finishing can add weight (a resin or a stiffening finish) or remove it (shrinkage tightens the cloth and raises GSM, while scouring and brushing can change it). Blends have their own yarn counts and densities. Filament and spun yarns do not follow the Ne system the same way, and the count may be written in denier instead, as the yarn guide explains.

The only figure that counts for acceptance is the one the lab measures on the delivered cloth, under the tolerance in the spec. See what GSM means in uniform fabric for how it is measured and what tolerance is usual.

How to use this when you compare quotes

Two quotes at the same GSM can hide different constructions: one with finer yarn and fewer threads, one with coarser yarn and more. They will feel and wear differently. Put the construction lines side by side, run the formula on each, and ask the seller to explain any quote where the result is far from the stated GSM. This pairs with the line-by-line comparison in uniform fabric pricing explained.

FAQ

Frequently asked questions

How do I estimate GSM from yarn count, EPI and PPI?

For cotton-system counts, GSM is about 23.25 × (EPI + PPI) ÷ Ne, before allowing 5 to 8 percent for crimp. Use it to cross-check a quoted weight against its construction line.

Is the formula exact?

No. Crimp, finishing, shrinkage and blend all move the real weight. It catches a quote that cannot be right, but the lab result on the delivered cloth is the one that counts.

What is crimp, and why does it add weight?

Crimp is the extra yarn length used when a thread goes over and under its neighbours instead of lying straight. More length means more weight than the bare formula counts.

What if the warp and weft counts are different?

Work out each direction separately: the threads per inch in that direction divided by its own count, times the constant, then add the two results.

My quote's GSM does not match the construction. What should I do?

Ask the seller to explain. Common reasons are a different count or density from the one written, or a heavy finish. If the explanation is vague, ask for the lab report on the delivered lot before you commit.