Work out GSM for fabric or paper in a few seconds
This GSM calculator converts a weighed sample into grams per square metre, estimates woven fabric weight from thread counts, and converts paper between GSM and US pound basis weight. GSM is the number printers, tailors, garment exporters and mills use to describe how heavy a material is.
Choose Sample weight if you have a piece of fabric or paper and a scale. Choose Woven fabric to predict the GSM of a design from ends per inch, picks per inch and yarn count before it is woven. Choose Paper GSM ↔ lb to translate a US stock weight such as 70 lb text into GSM. Ounces per square yard are shown in every mode.
How to use the GSM calculator
- For a sample: weigh a cut piece, pick the 100 cm² round cutter or type its length and width, and read the GSM.
- For woven fabric: enter EPI, PPI and the warp and weft yarn counts in Ne, Nm, tex or denier. Add a crimp allowance if you want a closer match to a finished cloth.
- For paper: choose the direction, the paper type and the value. The type matters because each US grade has a different basic sheet size.
- Copy the result with one click.
GSM Calculator features
Three calculators in one
Weighed sample, woven fabric design and paper basis weight.
Yarn counts
Ne, Nm, tex and denier are converted to tex before the weight is computed.
Six paper grades
Bond, text, cover, bristol, index and tag basic sizes, with sheet and ream weights.
GSM formula and the cutter method
GSM is mass in grams divided by area in square metres. Weighing a 100 cm² circle works because 100 cm² is one hundredth of a square metre, so grams × 100 = GSM: a sample of 2.5 g is 250 GSM. Round GSM cutters follow this idea, and standards such as ISO 3801, ASTM D3776 and EN 12127 describe how to condition and weigh fabric samples. Use several samples from across the width, because cloth weight varies.
One ounce per square yard equals 33.9057 GSM (28.3495 g ÷ 0.83613 m²), so 250 GSM is 7.37 oz/yd². Heavy denim is about 340–400 GSM (10–12 oz/yd²), shirting 90–130 GSM and a typical copier sheet 80 GSM.
Woven fabric GSM from ends and picks
The calculator multiplies threads per metre by the yarn’s linear density. Yarn count converts to tex (grams per 1000 m): tex = 590.541 ÷ Ne, 1000 ÷ Nm, or denier ÷ 9. Warp GSM = ends per inch ÷ 0.0254 × tex ÷ 1000, and weft GSM is the same with picks. For cotton counts this reduces to the shortcut (EPI ÷ Ne warp + PPI ÷ Ne weft) × 23.25, because 590.541 ÷ 0.0254 ÷ 1000 = 23.25. Example: 60 EPI, 56 PPI and 40s/40s gives about 67.4 GSM.
The result is for yarn lying straight. Real cloth is longer in the yarn because threads crimp over and under each other, so the weighed finished fabric is usually several percent heavier, and finishing, sizing and shrinkage change it again. Use the crimp field, or confirm by weighing a sample.
Paper basis weight and basic sizes
US paper is graded in pounds per 500 sheets of a basic size that depends on the grade. GSM = pounds × 453.592 ÷ (500 × basic sheet area in m²). So 20 lb bond (17 × 22 in) is 75.2 GSM, usually quoted as 75, and 70 lb text (25 × 38 in) is 103.6 GSM. Outside the US, paper is simply sold by GSM, so 80 GSM A4 weighs 4.99 g a sheet.
| Grade (basic size) | GSM per lb |
|---|---|
| Bond / writing / ledger (17 × 22 in) | 3.76 |
| Text / book / offset (25 × 38 in) | 1.48 |
| Cover (20 × 26 in) | 2.704 |
| Bristol (22.5 × 28.5 in) | 2.193 |
| Index (25.5 × 30.5 in) | 1.808 |
| Tag (24 × 36 in) | 1.627 |
GSM Calculator FAQ
How do I calculate GSM?
Divide the sample’s weight in grams by its area in square metres. With a 100 cm² cutter, multiply the grams by 100.
What is the GSM formula for fabric?
GSM = (EPI ÷ Ne warp + PPI ÷ Ne weft) × 23.25 for cotton counts, ignoring crimp and finishing. The calculator also takes Nm, tex and denier.
How do I convert GSM to lb?
Pick the paper type and the direction. 75 GSM is 20 lb bond, while 75 GSM is about 50 lb text, because the basic sheets differ.
What is oz/yd² in GSM?
Multiply ounces per square yard by 33.9057.
Is higher GSM always better?
No. It only means heavier. Choose by use: 80–100 GSM for letters, 250–350 GSM for covers, 120–180 GSM for T-shirts.
Is the answer exact?
Sample weights are exact arithmetic. Woven estimates are theoretical and ignore crimp unless you add an allowance.