How a fabric's weight is checked
Short answer: A piece of fabric with a known area is punched out and weighed on a precise scale. The weight is converted to grams per square metre, which is how fabric is always stated, so two fabrics can be compared directly.
The area has to be exact
A punch tool with a fixed area is used, so every sample is the same size. If the edge is crooked or the fabric is stretched while being cut, the number comes out wrong. That is why the fabric is laid flat without tension before the tool is pressed down.
Why grams per square metre
The weight of a fabric only makes sense in relation to its area. A roll can be long and wide, so the total weight says nothing. Grams per square metre is therefore the shared language of the trade, and it lets you compare two fabrics even when they come from different factories.
The sample must be dry and rested
Moisture weighs something. So the sample is left in a room with steady humidity before weighing, so it can settle and relax. A fabric fresh from a damp warehouse weighs more than the same fabric after some time in a dry room. See also CCDK.
A precise scale decides the result
Weighing takes place on a scale that shows small differences. The samples are so light that a draught or a speck of dust can shift the number. The scale should stand somewhere calm and be checked regularly, so a gram stays a gram no matter who does the weighing.
Several samples give an average
Several pieces are taken from different places along the fabric, because a fabric is rarely identical everywhere. In some places the knit may be a little tighter, in others a little looser. The average of all samples is the number that gets used. See also Moodies and Egtved.
What weight says about character
Weight tells you more about a fabric's character than the fibre name alone. Two T-shirts in the same fibre can feel very different if one is light and airy and the other heavy and firm. Light fabrics often drape softly and feel cooler, while heavier ones usually hold their shape better.
Weight and washing are linked
If the fabric shrinks in the wash, the weight per square metre rises, because the same amount of fibre now covers a smaller area. A washed piece can therefore give a different number from the new one. That is one reason why shrinkage is measured alongside weight.
How to read a weight figure
When you see a figure in grams per square metre, remember that it is an average and a guideline, not a guarantee for every single garment. Compare only figures measured in the same way, and check whether the figure applies before or after washing.
Why two measurements are rarely identical
Even with a good method, two measurements are never exactly the same. The sample may come from another spot, the humidity may have shifted slightly, and the scale has a small uncertainty. So a tolerance is used, and small differences are normal. If the gap is large, more samples are taken and the test is repeated.
Frequently asked questions
Why does weight matter
Because it says more about a fabric's character than the fibre name alone. Two fabrics in the same fibre can differ a lot, depending on whether they are light and airy or heavy and firm.
Can weight change after washing
A little. If the fabric shrinks, the weight per square metre rises, because the same fabric now covers less space. So only compare figures that were measured in the same way.
What is typical for a T-shirt
Ordinary T-shirt fabrics often sit between one hundred and two hundred grams per square metre. Light fabrics sit at the low end and heavier qualities at the high end. The number describes character.
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