Guides · Fabrics
What GSM means on a T-shirt and which weight to buy for heat
GSM in plain terms
GSM means grams per square meter. It is how much one square meter of the fabric weighs.
Higher GSM means heavier, denser fabric. Lower GSM means lighter, thinner fabric. It does not measure quality. It measures weight.
Most tees you see are between 120 GSM and 240 GSM. Packaging might say ounces instead. A 6.5 oz tee is roughly 220 GSM. Both numbers describe the same thing.
When you log a tee in moggers, fill in the GSM field if the brand lists it. Over time you will see which weight you actually wear in heat.
How weight changes the shirt
Weight affects three things you feel right away.
First, opacity. Lightweight tees under 150 GSM are often sheer, especially in white. Midweight tees around 180 to 200 GSM are usually opaque without being hot.
Second, drape. Heavyweight tees 220 GSM and up hold their shape. The shoulder sits where it should. The body does not cling when you sweat. Lightweight tees drape closer to the body and move more.
Third, heat. Heavier fabric holds more heat. Lighter fabric lets air through faster. In 90°F with humidity, that difference matters.
I ordered a 240 GSM “premium blank” after staring at product shots for a week. On the hanger it looked like it would mog every other tee I owned. First August afternoon outside, it felt like a damp towel. Nobody looks expensive when they are cooked. I still like the cut. I just wait until the sun drops.
Which GSM to buy for hot weather
For Miami and similar heat, most people live in two ranges.
150 to 180 GSM for max breathability. Good for undershirts, gym-to-street tees, and days when you know you will be outside. Look for open weaves and combed cotton or cotton blends. They dry faster.
180 to 210 GSM for everyday wear. This is the sweet spot for streetwear in heat. Opaque, not see-through, holds shape after washes, but does not cook you. A 6 oz tee sits right here.
220 GSM and up for structure. Heavyweight tees look great and last longer. They work for nights, indoor days, and when you want that boxy fit to stand on its own. For all-day outdoor wear in August, they run hot.
If you sweat a lot, lean lighter. If you care about shape and longevity, lean midweight.
How to check GSM when the brand does not list it
Many brands list GSM. Many do not. You can still get close.
Check the ounces. If it says 6.5 oz, multiply by 33.9 to get GSM. So 6.5 oz is about 220 GSM.
Check the description. Words like heavyweight, burly, or structured usually mean 200 GSM plus. Words like lightweight, featherweight, or tissue usually mean under 160 GSM.
Feel the hem. Pinch the bottom hem between thumb and finger. If you can barely feel it, it is light. If it feels like a thin towel, it is heavy.
Wash test. After one cold wash, heavyweight tees keep their width. Lightweight tees often shrink a little in length and get softer.
Log how hot it wears in moggers after a real day. Your own rating beats any product page.
When heavyweight still makes sense in heat
Heavyweight is not wrong for hot weather. You just have to pick when to wear it.
It works when you are mostly indoors, or out at night. It also works when the fit is relaxed and there is airflow around the body. An oversized heavyweight tee with room at the sides can feel cooler than a tight lightweight tee.
Fabric matters too. A 210 GSM tee in 100% cotton wears hotter than a 210 GSM blend with some breathability built in. Look at fiber content along with weight.
On a Saturday that starts in AC and ends outside after 8, I grab the heavyweight. Structure holds. That is when heavyweight actually mogs. On a weekday walking between buildings at 2 p.m., midweight or lighter. Same closet. Different job. Sweating through a “better” shirt is not a flex.
Quick takeaways
- GSM is fabric weight. Higher is heavier and usually more opaque and structured.
- For hot weather, 150-180 GSM is coolest, 180-210 GSM is the everyday balance.
- If GSM is not listed, use ounces, feel, and your own heat rating to judge.