Fabric GSM calculator
Fabric weight converts between g/m² and oz/yd² by a factor of 33.905747 — exactly one ounce, 28.349523125 g, spread over one square yard, 0.83612736 m² — so a 150 g/m² cotton is 4.42 oz/yd². Ounces per RUNNING yard is a different measure that depends on the roll width, and momme is the silk unit at 4.3399 g/m² each. The converter below handles all four, says what weight class a fabric falls into, and works out the weight from a weighed swatch when there is no label.
A fabric weight, in any of its units
No label? Weigh a swatch
150 g/m²
4.42 oz/yd² · Poplin, twill, jersey, linen, most dressmaking and quilting.
- Grams per square metre
- 150 g/m²the cloth itself
- Ounces per square yard
- 4.42 oz/yd²the US standard
- Ounces per running yard
- 6.77 oz/ydat 140 cm wide
- Momme
- 34.6 mmthe silk unit
- Weight of 3 m
- 630 guseful for postage
How we got this
- Weight as entered — 150.0 g/m²150 g/m²
- Ounces per square yard — 4.42 oz/yd²150.0 g/m² × 0.83612736 m² ÷ 28.349523125 g
- Ounces per running yard at 140 cm — 6.77 oz/yd150.0 g/m² × 0.9144 m × 1.400 m ÷ 28.349523125 g
- Momme — 34.6 mm150.0 g/m² × 104.5159 m² ÷ 453.59237 g
- Weight of 3 m at 140 cm — 0.63 kg150.0 g/m² × 3.00 m × 1.400 m
What the number describes
Short definitions of GSM, running yard and momme are in the glossary. This section is about why the distinction between them matters.
Grams per square metre is the weight of a piece of the fabric one metre square. It says nothing about how wide the roll is, how the cloth was cut, or how long a piece you have — which is precisely why it is useful. Two fabrics quoted in g/m² can be compared directly; almost nothing else about a fabric listing can.
It is not a measure of quality, and it is only loosely a measure of thickness. A dense, tightly woven silk can weigh the same as a loose, lofty cotton twice its bulk. What it does predict well is behaviour: whether a fabric will fall into soft folds or hold a shape, whether a curtain will hang straight, whether a bag will stand up on its own.
The conversion, exactly
One ounce is 28.349523125 grams by definition, and one square yard is 0.83612736 square metres, since a yard has been exactly 0.9144 m since 1959. Divide the first by the second and one ounce per square yard is 33.905747 g/m². The trade rounds it to 33.9, which is close enough for choosing a fabric and not close enough to build a converter on.
Momme, the silk unit, is defined the same way from a different piece: the weight in pounds of a length 100 yards by 45 inches. That works out at 4.3399 g/m² per momme, so the 19-momme charmeuse sold for bedding is about 82 g/m² — a light fabric by any general measure, which is why silk keeps a scale of its own.
| Step | Working | Result |
|---|---|---|
| Weight as entered | 150 g/m² | 150.0 g/m² |
| Ounces per square yard | 150.0 g/m² × 0.83612736 m² ÷ 28.349523125 g | 4.42 oz/yd² |
| Ounces per running yard at 140 cm | 150.0 g/m² × 0.9144 m × 1.400 m ÷ 28.349523125 g | 6.77 oz/yd |
| Momme | 150.0 g/m² × 104.5159 m² ÷ 453.59237 g | 34.6 mm |
| Weight of 3 m at 140 cm | 150.0 g/m² × 3.00 m × 1.400 m | 0.63 kg |
Why two "12 oz" fabrics are different cloths
This is the one that costs people money. Denim and canvas are usually sold by the ounce per running yard — the weight of one yard off the roll, whatever the roll happens to be. Everything else is sold by the ounce per square yard.
A 12 oz denim on a 60-inch roll is 244 g/m². The same 12 oz quoted on a 44-inch roll is 333 g/m² — a substantially heavier cloth, because the same weight is spread over less width. Nothing on either listing will tell you this; the only defence is to convert both to g/m² before comparing.
What each weight is good for
| Band | g/m² | oz/yd² | Typical fabrics |
|---|---|---|---|
| Very light | under 80 | under 2.4 | Chiffon, organza, voile, fine lining. Sheer; needs care to sew. |
| Light | 80–120 | 2.4–3.5 | Lawn, batiste, shirting, quilting cotton, dress cotton. |
| Medium | 120–200 | 3.5–5.9 | Poplin, twill, jersey, linen, most dressmaking and quilting. |
| Heavy | 200–300 | 5.9–8.8 | Denim, drill, curtain fabric, light upholstery, bag fabric. |
| Very heavy | 300–400 | 8.8–11.8 | Upholstery weight, heavy canvas, outdoor fabric, coating. |
| Extra heavy | over 400 | over 11.8 | Heavy upholstery, tarpaulin, rug and carpet backing. |
The bands are conventions rather than standards, and the boundaries are soft — a 205 g/m² cotton is not meaningfully different from a 195 g/m² one. Treat them as a way of translating a number into an expectation, not as a specification.
Weighing a fabric with no label
Most fabric in a stash has no label, and the answer is a pair of scissors and a kitchen scale. Cut a square of a known size, weigh it, and divide the weight by the area. A 10 × 10 cm square is a hundredth of a square metre, so the arithmetic is simply grams × 100.
The part worth understanding is the precision. A domestic scale reads to 0.1 g, and how much that resolution is worth depends entirely on how big a swatch you cut.
| Swatch | It weighs | Works out at | Best you can say |
|---|---|---|---|
| 5 × 5 cm | 0.3 g | 140 g/m² | ± 40 g/m² |
| 10 × 10 cm | 1.4 g | 140 g/m² | ± 10 g/m² |
| 20 × 20 cm | 5.6 g | 140 g/m² | ± 2 g/m² |
A 5 cm square tells you almost nothing: the band it produces spans two weight classes. A 20 cm square pins the figure down to a couple of per cent. Cut the biggest swatch you can spare, cut it square, and weigh it dry — a fabric that has been sitting in a damp room reads heavy.
How to use this
- Find the weight on the label. Metric listings give g/m² or gsm. US listings usually give oz/yd², and denim or canvas often gives ounces per running yard instead.
- Check which ounce it is. Per square yard describes the cloth. Per running yard describes a yard off that particular roll, so it changes with the width.
- Or weigh a swatch. Cut a 10 by 10 cm square as accurately as you can and weigh it. Grams times 100 is the weight in g/m².
- Read the weight class. The band matters more than the exact figure: it is what tells you whether a fabric will hang, drape or stand up.
- Work out what your piece weighs. Length times roll width times g/m². Useful for postage, and for knowing whether a curtain track will take it.
What the weight will not tell you
- How it drapes. Weight and drape are different properties. A crisp organza and a fluid crepe de chine can weigh the same and behave nothing alike, because drape depends on fibre, twist and weave as much as mass.
- How hard-wearing it is. Upholstery durability is measured in rub tests, not grams. A heavy loose weave can wear out faster than a lighter tight one.
- How thick it is. A lofty brushed cotton and a dense poplin at the same weight differ in thickness by a factor of two, which matters for seam bulk and for whether a bag will turn through.
- Whether it will shrink. Nothing about weight predicts that. Wash a test piece.
Converting the length as well? Yards to metres and the fabric width converter handle the other two axes, and the seam allowance calculator deals with the difference between what you cut and what you get.
Common questions
- What does GSM actually measure?
- Grams per square metre — the weight of a piece of the fabric one metre by one metre. It describes the cloth itself, independently of how wide the roll is or how it was cut, which is why it is the only weight figure that lets two fabrics be compared directly.
- How do I convert GSM to ounces per square yard?
- Divide by 33.905747. That figure is exact rather than a trade approximation: one ounce is 28.349523125 g by definition and one square yard is 0.83612736 m², so 150 g/m² is 4.42 oz/yd² and 350 g/m² is 10.32 oz/yd².
- Why do two "12 oz" fabrics feel different?
- Because one is probably quoted per square yard and the other per running yard. A running yard of 150 cm cloth contains far more fabric than a running yard of 112 cm cloth, so the same ounce figure describes two different weights. Denim and canvas are usually sold the second way.
- How do I find the weight of fabric with no label?
- Cut a square of a known size — 10 by 10 cm is ideal — and weigh it on a kitchen scale. Multiply the grams by 100 and you have the weight in g/m². A scale reading to 0.1 g gives you ±10 g/m² at that swatch size, which is close enough to place a fabric in its weight class.
- What is momme?
- The silk unit: the weight in pounds of a piece 100 yards long by 45 inches wide. One momme is 4.3399 g/m², so the 19-momme charmeuse sold for bedding is about 82 g/m² — a light fabric by any other measure, which is why silk weight has a scale of its own.
Related tools
Fabric weight chart
Weight bands in g/m² and oz/yd², and what each band is actually used for.
Fabric width converter
Pattern written for one bolt width, fabric bought at another — work out the equivalent length.
Seam allowance calculator
Finished size to cut size — and what a different allowance does to the garment you end up with.
Yards to metres
Convert a pattern written in yards to metres, with the common cut lengths tabulated.