Cloth is sold by weight, not by thickness. Find out how heavy the cloth in your own t-shirt is, then see how it stacks up against the flannel we have asked a mill to weave.
Put it on the kitchen scale and write down the grams. If your scale only does ounces, switch it. If it cannot, ask a grown-up to find one that can. Write the number down before you do anything else.
Smooth the shirt out on a table, front up. Measure straight across at the chest, from one side seam to the other. Then measure from the top of the shoulder down to the bottom hem. Both in centimetres.
Write both down. Do not measure the sleeves. They come in a minute.
A shirt is two layers of cloth, a front and a back. So the area is width times length, then times two. That gives square centimetres.
There are ten thousand square centimetres in one square metre, so divide by ten thousand to get square metres.
Grams divided by square metres is the weight of one square metre of your t-shirt's cloth. That is its GSM. The box below does the sums if you would like to check yours.
You ignored the sleeves, the hems, the neckband and the seams, and all of those weigh something. So your number is a little off. A mill weighs a flat cut piece of the cloth on its own, which is why theirs does not have this problem and yours does. Knowing how wrong an answer is, and why, is the first thing an inspector learns.
Type in what you measured. Nothing leaves this page.
Fill in all three boxes and the answer shows up here.
Our target: 300 grams a square metre, give or take 20.
What we asked for
300 grams a square metre
That is the finished weight of the Greenbush Check flannel in our tech pack, give or take 20, so anything from 280 to 320 passes. In the old money some mills still use, that is about 8.3 to 9.4 ounces to the square yard.
We do not have a weight for a t-shirt to put next to it, and we are not going to guess one. Your shirt is the other half of the comparison, which is why you are the one with the scale.
The flannel has not been woven yet, so 300 is what we asked for, not what anyone has measured. When a mill sends a sample, somebody will weigh it exactly like this.
That is the end of this one
The word for what you just did is gsm.
GSM means grams per square metre, and it is how the whole trade says how heavy a cloth is. Two cloths can look the same and feel the same through a shop window, and the number still tells you which is the thicker, warmer, more expensive one. It is the first line of our flannel's spec.
Where to go now