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You'll usually see canvas identified in a fabric store by weight, such as 4 oz. or 10 oz. If you have a piece of canvas and want to find out how many ounces it is, you can weigh it and calculate how it would be labeled.
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Usually, the number of ounces refers to how many ounces per square yard. However, some laws define a square yard of canvas as 36 inches by 29 inches, rather than 36 inches by 36 inches. You can calculate the ounces both ways, and the difference probably won't be great enough to affect a typical sewing project. However, if your calculation doesn't exactly agree with a label, this might be the reason.
Select a sample of canvas that's a square or rectangle. If you can cut a piece exactly 36 inches by 36 inches or 36 inches by 29 inches, cut a piece that size and weigh it in ounces. However, if your canvas isn't that large or it's larger and you don't want to cut it, you can figure the number of ounces from any size sample.
Measure the width and length of the sample in inches with a measuring tape. Multiply those two numbers together. If you want to figure the ounces per normal square yard, divide the result by 1,296. If you want to figure the ounces per 36-by-29-inch square, divide the result by 1,044. The result will be the number of square yards.
Weigh the sample on an accurate scale that reads in ounces. If the scale reads in pounds and ounces, multiply the number of pounds by 16 and add the number of ounces.
Divide the number of ounces by the number of yards to determine the weight of the fabric.
- "The Big Book of Boat Canvas"; Karen Lipe; 1991
- "The New Artist's Manual"; Simon Jennings; 2005
- "Tipis, Tepees, Teepees: History and Design of the Cloth Tipi"; Linda A. Holley; 2007
- Illinois General Assembly: Cotton Duck or Canvas Act
- Minnesota Office of the Revisor of Statutes: 2009 Minnesota Statutes 325F.35