GSM Explained: Fabric and Paper Weight Without the Guesswork
One ounce per square yard is 33.906 GSM, exactly. US paper weights are harder, because every grade is weighed at a different sheet size.
3 October 2026 · 6 min read · Reference
GSM means grams per square metre. It is the weight of a single square metre of the material, which makes it the one honest way to compare fabric or paper, regardless of roll width or sheet size.
Fabric: the only factor you need
1 oz/yd² = 33.906 g/m²
Divide GSM by 33.906 for ounces per square yard, or multiply the other way. Use the GSM converter for exact figures.
| GSM | oz/yd² | Typical use |
|---|---|---|
| 110 | 3.2 | Lightweight summer t-shirt |
| 150 | 4.4 | Standard t-shirt |
| 180 | 5.3 | Good-quality t-shirt |
| 220 | 6.5 | Heavyweight tee, light hoodie |
| 280 | 8.3 | Sweatshirt fleece |
| 340 | 10.0 | Heavy hoodie, canvas |
| 400 | 11.8 | Denim, upholstery |
| 600 | 17.7 | Luxury bath towel |
Higher GSM is not automatically better. A 180 GSM shirt in combed cotton outlasts a 220 GSM shirt in coarse fibre, and a heavy towel takes longer to dry.
Paper: why 20 lb and 50 lb can be the same sheet
US mills state basis weight: the weight of 500 sheets at that grade's own parent size. Each grade uses a different parent size, so the numbers are not comparable between grades.
| Grade | Parent sheet | Multiply lb by |
|---|---|---|
| Bond / writing | 17 × 22 in | 3.76 |
| Text / book / offset | 25 × 38 in | 1.48 |
| Cover / card | 20 × 26 in | 2.70 |
| Index | 25.5 × 30.5 in | 1.81 |
That is why 20 lb bond (75 GSM) and 50 lb text (74 GSM) are essentially the same paper under two names.
| Common paper | GSM |
|---|---|
| 20 lb bond — office copy paper | 75 |
| 24 lb bond — letterhead | 90 |
| 70 lb text — brochure | 104 |
| 100 lb text — magazine cover | 148 |
| 65 lb cover — flyer, light card | 176 |
| 80 lb cover — business card | 216 |
| 100 lb cover — premium card | 270 |
For reference, a typical business card is 300–400 GSM, a postcard 250–350 GSM, and a wedding invitation 250–300 GSM.
Measuring GSM yourself
Cut a 10 × 10 cm square, which is one hundredth of a square metre, and weigh it in grams. Multiply by 100 and you have the GSM. A kitchen scale reading to 0.1 g is accurate enough for fabric.
For paper, weigh a known number of sheets of a known size instead: GSM = total grams ÷ (sheets × sheet area in m²).
Thickness is a separate question
GSM is weight, not thickness. Paper thickness is quoted in points (thousandths of an inch) or microns, and two sheets of the same GSM can differ in bulk depending on how tightly the fibres are pressed. For a card that feels substantial, check both.
Related conversions
This article is for general information. Please verify figures against the relevant standard before using them in critical work. About accuracy