Canvas Tarps

Canvas tarps are a time-honored way to protect your valuables from sun and water. The word canvas derives from the word cannabis, because the cloth was made from hemp before cotton was a commercially viable product. The word tarpaulin was formed from a combination of "tar" and "palling" and referred to canvas that had been coated with tar to make it waterproof for use aboard ships. Hemp is no longer widely used in the textile industry, and we now have better (and less messy) products than tar for waterproofing canvas fabrics, which are now commonly made from cotton.

Measuring Canvas By Weight

Canvas that is measured by weight is sold based on the weight of one square yard of the cloth. Very lightweight canvas cloth can weigh as little as 7 oz. per square yard, while canvas cloth for everyday light use starts at around 12 oz. per square yard.

Finished canvas tarps can weigh more after they are treated with waterproofing material and/or UV light resistant coatings. The coatings can add several ounces per square yard to the weight of the cotton canvas tarp material.

Canvas Duck Tarp

Canvas duck tarp material may also be sold under a numbering system, in which the lower numbers indicate heavier, more dense cloth. Number one canvas duck cloth is very heavy duty canvas, while number ten canvas cloth is fairly light. It may also be single fill or double fill canvas, another measure of the thread density of the canvas cloth.

Lower Numbers Mean Heavier Canvas Tarp

Why is it that a lower number means a heavier canvas tarp cloth? The explanation has to do with the weight of a square yard of cloth and the number 19. If a yard of cloth weighs 11 ounces, it is #8 canvas cloth (19 minus 11 equals 8). If a yard of cloth weighs 18 ounces, it is #1 canvas cloth. #8 is a fairly lightweight canvas, and #1 is heavy canvas.

Why 19? Your guess is as good as mine.

What happens if a square yard weighs 19 ounces or more? There's an extended system for measuring the extra heavy duty canvas tarp material, called "naught duck" measurement. At 19 ounces per yard, it is 1/0 naught duck cloth, at 20 ounces, it is 2/0 naught duck, etc.

I have also seen reference to measuring the weight of a 36" by 22" square of cloth when calculating numbered duck or naught duck canvas cloth weight. It seems that duck canvas is more densely woven than ordinary canvas, or maybe the information was incomplete.

And then there is army duck canvas, which is measured in ounces with numbers like 10.10 army duck or 12.29 army duck canvas.

Are you sorry you asked about canvas cloth weight measurement yet? Canvas cloth may or may not be canvas duck cloth. It might be single fill or double fill canvas duck, and it might be measured by the weight of a square yard, or the weight of almost a square yard. That weight might be used directly as the unit of measurement, or it might be subtracted from the number 19, or it might go into a whole different measurement system if the weight of a square yard (or almost a square yard) is greater than or equal to 19 ounces.