# 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.

Source: https://fabricmeasure.com/conversions/fabric-gsm-calculator/
Last updated: 2026-08-20 (method v1)
Published by FabricMeasure.

---

## The formula

```
gsm            = ozPerSquareYard x 33.905747
gsm            = momme x 4.3399
gsm            = ozPerRunningYard x 28.349523125 / (0.9144 m x rollWidth m)
pieceWeight_g  = gsm x length_m x rollWidth_m
gsmFromSwatch  = swatchGrams / swatchArea_m2
```

The constants are exact, not the trade rounding: one ounce is 28.349523125 g and one square
yard is 0.83612736 m2 by definition, so one oz/yd2 is exactly
33.905747 g/m2 rather than 33.9. Momme is the weight in pounds of a piece
100 yards by 45 inches.

OUNCES PER RUNNING YARD IS NOT OUNCES PER SQUARE YARD. The first depends on the roll width,
so the same "12 oz" denim is a different cloth at 44 in than at 60 in. Convert both to g/m2
before comparing anything.

## Weight classes

| Band | g/m2 | Typical fabrics |
| --- | --- | --- |
| Very light | under 80 | Chiffon, organza, voile, fine lining. Sheer; needs care to sew. |
| Light | 80-120 | Lawn, batiste, shirting, quilting cotton, dress cotton. |
| Medium | 120-200 | Poplin, twill, jersey, linen, most dressmaking and quilting. |
| Heavy | 200-300 | Denim, drill, curtain fabric, light upholstery, bag fabric. |
| Very heavy | 300-400 | Upholstery weight, heavy canvas, outdoor fabric, coating. |
| Extra heavy | over 400 | Heavy upholstery, tarpaulin, rug and carpet backing. |

## Weighing an unlabelled fabric

Cut a square of known size and weigh it. A 10 x 10 cm swatch is a hundredth of a square
metre, so grams x 100 is the weight in g/m2. A scale reading to 0.1 g gives +/-10 g/m2 at
that size; a 5 cm swatch gives +/-40, which spans two weight classes and is not worth doing.

## Worked example

150 g/m2 on a 140 cm roll, with 3 m of it.

| 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 |

## What weight does not tell you

- Drape: a crisp organza and a fluid crepe can weigh the same and behave differently.
- Durability: upholstery wear is measured in rub tests, not grams.
- Thickness: a lofty weave and a dense one at equal weight differ twofold in bulk.
- Shrinkage: nothing about weight predicts it. Wash a test piece.

## 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](https://fabricmeasure.com/charts/fabric-weight-chart/): Weight bands in g/m² and oz/yd², and what each band is actually used for.
- [Fabric width converter](https://fabricmeasure.com/conversions/fabric-width-converter/): Pattern written for one bolt width, fabric bought at another — work out the equivalent length.
- [Seam allowance calculator](https://fabricmeasure.com/calculators/seam-allowance-calculator/): Finished size to cut size — and what a different allowance does to the garment you end up with.
- [Yards to metres](https://fabricmeasure.com/conversions/yards-to-metres/): Convert a pattern written in yards to metres, with the common cut lengths tabulated.