Fabric Weight and Conversions
Today we have a guest entry from Jennifer Ennis. Jennifer is a DE from Winnipeg Canada. She has worked in the garment industry for both an importer and domestic producer. Her educational background is diverse mix of textile science, design and economics (sustainable development) which includes, in her opinion, far too much time in front of a HunterLab colorimeter. Thanks Jenn!
Let’s talk about fabric weight. If you’ve been confused with converting weights of fabrics, most often described as “grams per square meter” or “ounces per square yard”, this should help you. Technically, both of these refer to “fabric mass”. I make this distinction only because if you try and look up test methods to determine weight (fabric mass) you’ll not find it. But okay, I am calling it “weight”.
Previously when I worked for a garment manufacturer, I was often working on fabric testing mostly because I paid attention in textile science class. It came in handy to save few rear ends during my time there so it is useful stuff to know (I‘d also like mention that I paid attention in design and economics too).
I tested fabrics from Asia, the United States and Europe (Italy specifically) and I have run across many ways weight was described. I would hesitate to suggest that fabrics were deliberately mislabeled to mislead people but based on what I’ve seen, I can’t say they weren’t either. For example, one mill told us the fabric was 14 oz and everyone assume it was per square yard when in fact it was per liner yard and ended up only weighing 12 oz/yd2. So it is important to understand what unit is being measured and always, if in doubt, clarify and verify.
In my experience, the two most common descriptions of weight were:
- GSM aka g/m2 = grams per square meter
- oz/yd2 = ounces per yard squared
I have also run across
- g/m or gram per linear meter
- oz/yd or ounces per linear yard,
- g/yd2 or gram per yard squared *
- oz/m2 or oz per meter squared *
* why in heaven’s name you would mix the two systems (imperial and metric) is beyond me but people do.
Gsm is the standard and I am not just saying this because I one of those weird people trained in new math and metric. Here are three reasons:
- Metric is ISO standard units and used in ASTM D3776-07 Standard Test Methods for Mass Per Unit Area of fabric (that is the test method you be asking a material testing lab to run)
- Equipment is inexpensive and commonly available for use in measuring these units, even in office situations.
- It is internationally understood (USA is one of the only countries not using metric system)
There is an easy way to convert gsm to oz/yd2.
Divide the gsm by 33.906 – really that is all.
To determine gsm from oz/yd2 you do the reverse – multiple by 33.906.
If it helps, this is what the formulas are based upon:
- 1 oz = 28.3495231 grams
- 1 yard = 0.9144 meters
- 1 yard squared = (.9144 m x .9144 m) =.83612736 meters squared
- 1 oz/yd2 = 28.3495231g/.83612736 m2 = 33.90574744 g/m2
- Rounded up to three decimal places it is 33.906
If you don’t like doing the math –I dislike doing calculations repeatedly– you may prefer to use tables to look things up. I know I do. To make it easier for you, I’ve attached a table I made (pdf 16kb) that shows conversion for the most common weights of 50 gsm to 689 gsm to oz/yd2. I recommend sticking it in a plastic protector sheet, storing it in a binder or attached to a cork board and you are all set.
If there is sufficient interest or questions, I can write another part to cover other conversions and perhaps another section on how to do internal approval testing and limitations. I’m thinking a good post would be about converting GSM to oz/linear yard in order to calculate for dye houses i.e. how many yards to make up x number pounds of fabric.