The weight of a single garment tells you something
Short answer: A t-shirt in size L typically weighs between 110 and 180 grams. Less than that and the fabric is thin. More and it is more densely knitted.
How to measure
Put the garment on a kitchen scale. Note the weight and the size together, because an XXL naturally weighs more than an S. Only compare the same size and the same type.
What the numbers mean
Under 110 grams in size L is very light and turns see through quickly. 130 to 160 grams is the ordinary everyday t-shirt. Over 180 grams is a thick, heavy fabric. See bamboo t-shirts for men.
When it is useful
When you are choosing between two garments that look the same in a photo. Weight is the only figure you can measure at home yourself. See bamboo t-shirts for women and bamboo clothing for men.
Frequently asked questions
Are heavy clothes always better
No. For summer and for underwear, light is better. Weight tells you what you get.
What about grams per square metre
That is the same figure seen differently. Your kitchen scale measures the whole garment.
Is the weight shown in an online shop
Rarely for clothing. That is why measuring at home is useful.