GSM / Fabric Weight Calculator
Convert fabric weight between GSM (g/m²) and ounces per square yard (oz/yd²).
Reviewed by the ToolNestr Editorial Team — July 2026
How the GSM conversion works
GSM (grams per square meter) and oz/yd² (ounces per square yard) both measure fabric density — how much a given area of fabric weighs — just in different unit systems. The conversion factor between them is fixed: 1 oz/yd² equals exactly 33.906 GSM, derived from converting ounces to grams and square yards to square meters. This calculator applies that constant in either direction.
Knowing this conversion matters because US-based patterns and fabric shops often list weight in oz/yd², while international suppliers, especially in Asia and Europe, list GSM — comparing two fabrics from different regions requires converting one to match the other first.
The 33.906 g/m² per oz/yd² conversion factor follows the standard textile-industry unit relationship referenced in ASTM D3776 (Standard Test Methods for Mass Per Unit Area of Fabric).
Worked example
A fabric listing shows 150 GSM and needs to be compared to a US supplier's oz/yd² fabric.
Real-world context
Sourcing fabric from international wholesale suppliers is the most common place this conversion gets used — a US-based small apparel brand comparing a domestic 6 oz/yd² denim against an overseas 200 GSM alternative needs both numbers in the same unit before the comparison means anything.
Pattern instructions increasingly list a recommended weight range to guide fabric substitution — a pattern calling for "6-8 oz/yd² mid-weight cotton" is directly useful to a US shopper but needs converting to roughly 200-270 GSM for a shopper only able to find fabric listed in metric weight.
Common misconceptions
"GSM tells you the fabric's fiber content." No. GSM only measures weight per area, not what the fabric is made of — a 150 GSM cotton and a 150 GSM polyester can feel completely different despite sharing the same GSM number.
"A higher GSM always means a stiffer fabric." Not necessarily. Weave structure and fiber type affect drape and stiffness as much as raw weight — a heavy, loosely woven fabric can still drape more softly than a lighter, tightly woven one.
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Frequently asked questions
What is GSM in fabric?
GSM stands for grams per square meter, a standard measure of fabric weight and density used worldwide, especially outside the US. Higher GSM means a heavier, denser fabric — quilting cotton is typically 120-150 GSM, while a heavy canvas can run 300-500 GSM or more.
Why does the US use oz/yd² instead of GSM?
Ounces per square yard is the traditional imperial measure used in the US textile industry, tied to the yard-based measurement system still common in American fabric retail, while most of the rest of the world uses the metric GSM standard.
Is heavier fabric always better quality?
Not necessarily — weight relates to fiber density and intended use, not inherent quality. A lightweight voile and a heavyweight denim can both be high quality for their respective purposes; GSM just helps you predict drape, structure, and durability for a specific project.
What GSM is good for a t-shirt versus a coat?
A typical t-shirt knit runs roughly 140-180 GSM, quilting cotton around 120-150 GSM, denim 200-500 GSM depending on weight, and a structured coating fabric often runs 400 GSM or higher.