How to check fabric GSM and width when knitted rolls arrive

When you buy knitted fabric by the kilo, two numbers decide how many garments each roll gives you: GSM (grams per square metre) and usable width. A heavier fabric than ordered means fewer metres per kilo, so fewer T-shirts. A narrower width than the one your marker was planned on means the lay no longer fits the table. That is why, next to visual inspection, measuring GSM and width is a mandatory check on arrival.

Why GSM drives the cost per garment

Let's assume you costed a T-shirt on a 180 g/m² single jersey with a consumption of 0.30 kg per piece. If the roll actually arrives at 195 g/m², the same pattern uses roughly 0.325 kg. An 8% difference sounds small, but across 1,000 T-shirts it adds up to about 25 kg of extra fabric for the same number of finished garments. The other way round, a GSM well below spec can give you a tee that is more see-through and limper than the approved sample, and customers notice.

GSM also affects shrinkage behaviour, opacity and drape. It is not just a number on the invoice.

How to measure GSM properly

The standard tool is a circular GSM cutter that cuts exactly 100 cm², plus a scale accurate to 0.01 g. The method:

1. Let the fabric condition for a few hours in the workroom, opened out and free of tension.
2. Cut samples from at least three positions across the width (near each edge and the centre), away from the roll end.
3. Weigh each sample and multiply by 100 to get g/m².
4. Average the results and record the minimum and maximum too.

Without a cutter you can cut a 10 × 10 cm square round a rigid template, but accuracy drops. Avoid measuring fabric straight after it has been stretched or compressed on the roll: knits relax, and the weight shifts slightly.

What tolerances are reasonable

In commercial practice, knitted fabric is commonly accepted within about ±5% on GSM, sometimes tighter for premium articles. Width tolerance is usually a few centimetres. What matters is that the tolerance is written on the order or on the fabric specification. Without it, you have no basis for a claim.

Also keep in mind the difference between greige weight and finished weight. The figure that matters to you is always the finished GSM, as the fabric arrives at your door.

Width: tubular or open

Many circular knits are supplied tubular, while others are slit open and stentered. When checking width:

• for tubular fabric, measure the tube lying flat and double it for the total width;
• for open-width fabric, measure the usable width inside the stenter pin holes or uneven edges, not edge to edge;
• measure at a minimum of three points along the roll, because width that wanders points to uneven finishing.

Width that varies a lot is often a warning sign of uneven shrinkage later, so it is worth pairing with a shrinkage test.

Checking length from weight

If you know GSM and width, you can estimate the linear metres on a roll: metres = net weight in kg × 1,000 / (GSM × width in m). For example, a 20 kg roll of 250 g/m² fabric at 1.80 m wide holds roughly 20,000 / (250 × 1.80) ≈ 44 m. If you get noticeably less when you unroll it, check net against gross weight (core tube and wrapping) and the real GSM.

A practical example

For oversized tees and garments with a more structured hang, a popular choice is petrol green single jersey at 250 g. At this weight, a few grams up or down are hard to see in the garment but easy to see in consumption, because each piece weighs more. It is worth weighing samples from each roll before you confirm the marker and costing on the real average, not the catalogue figure.

If you want to see or test fabric before production, you can buy from stock with no minimum, and for specific weights or shades you can send us a quote request. Details of the articles in our single jersey range are on the family page.