Fabric weight is quoted in two main units. Most of the world uses grams per square meter (GSM). Denim mills, many North American buyers and some woven fabric suppliers use ounces per square yard (oz/yd²). Converting between them is simple once you know the factor.
The conversion#
Rounded versions are common in daily use: divide GSM by 34, or multiply GSM by 0.0295. For quick talk on the floor these are fine. For specifications, test reports and costing, use 33.906.
Where 33.906 comes from#
The factor is not a convention; it follows from the unit definitions:
- 1 ounce (avoirdupois) = 28.3495 g
- 1 yard = 0.9144 m, so 1 square yard = 0.9144 × 0.9144 = 0.836127 m²
- 1 oz/yd² = 28.3495 g ÷ 0.836127 m² = 33.906 g/m²
Worked examples#
Conversion table#
| oz/yd² | GSM | oz/yd² | GSM |
|---|---|---|---|
| 3 | 101.7 | 9 | 305.2 |
| 4 | 135.6 | 10 | 339.1 |
| 5 | 169.5 | 11 | 373.0 |
| 6 | 203.4 | 12 | 406.9 |
| 7 | 237.3 | 13 | 440.8 |
| 8 | 271.2 | 14 | 474.7 |
Area weight is not linear weight#
Some suppliers quote ounces per linear yard: the weight of one yard of fabric at its full width. That number depends on width, so it cannot be converted to GSM without knowing the width.
A 10 oz/yd² fabric that is 60 inches wide weighs 10 × 60 / 36 = 16.7 oz per linear yard. If a price sheet says "16 oz" without saying which, ask before comparing offers.
Other units you may meet#
Fabric weight sometimes arrives in other forms. These are the conversions that come up most often:
| Unit | Meaning | Convert to GSM |
|---|---|---|
| g/m² (GSM) | Grams per square meter | Already GSM |
| oz/yd² | Ounces per square yard | × 33.906 |
| g per linear meter | Weight of one meter at full width | ÷ width in meters |
| oz per linear yard | Weight of one yard at full width | × 33.906 × 36 ÷ width in inches |
| Momme (silk) | Traditional silk weight unit | × about 4.34 |
For knit fabrics bought by weight, merchandisers also think in meters per kilogram: 1000 ÷ (GSM × width in meters). A 180 GSM fabric 1.8 m wide gives 1000 ÷ (180 × 1.8) = 3.09 m per kg. That number is handy when a woven-style consumption (in meters) must be turned into a knit booking (in kilograms).
Why the conversion matters in practice#
- Sourcing comparisons. Two offers for "the same" denim, one in ounces and one in GSM, can only be compared after conversion with the same factor.
- Testing reports. Laboratories report in the unit the method uses. A report in GSM against a tech pack in ounces needs converting before a pass or fail decision.
- Costing. Knit fabric is priced per kilogram, so weight feeds directly into consumption and cost. Use the fabric GSM article for measurement and the GSM chart for typical weights.
Common mistakes#
- Using 34 as the factor on a specification. It overstates GSM by about 0.3%, which is small but becomes a dispute when the tolerance is tight.
- Mixing up area and linear weight in fabric offers.
- Converting a GSM measured on a wet or unconditioned sample. Fix the measurement first, then convert.
Use the GSM to oz/yd² converter or the oz/yd² to GSM converter for exact values and a printable reference table.
Related guides#
- Yarn count: the other number that decides how heavy a fabric will be.
- List of top 100 denim jeans brands: denim, the fabric most often sold by ounces per square yard.
- Different types of fabric for dresses and clothing: typical weights for everyday clothing fabrics.
- Single jersey fabric: T-shirt jersey, one of the most common GSM conversions in buyer specs.