Understanding what that thickness actually means helps you decide whether a 20 mil tarp is worth the extra weight and cost for your specific project.
What Does “Mil” Mean When Measuring Tarp Thickness?
“Mil” is a unit of measurement equal to one-thousandth of an inch (0.001 inch). It is not shorthand for millimeter, and confusing the two leads to wildly wrong expectations. A 20 mil tarp is not 20 millimeters thick—that would be nearly an inch. Instead, 20 mil equals 0.020 inches, roughly the thickness of a heavy credit card.
For comparison, a standard painter’s tarp might run 2 to 5 mils, while heavy-duty options start around 10 mils. At 20 mils, you’re in super heavy-duty territory, meant for construction sites, long-term equipment storage, and transport covering.
What Can You Expect From a 20 Mil Tarp?
Retailers and manufacturers position 20 mil tarps as heavy-duty or super heavy-duty products. Common specs include polyethylene construction, UV resistance, and waterproofing. Here’s what typical listings show for a 20 mil tarp’s full build:
- Thickness: 20 mil (0.020 in / 0.508 mm)
- Material weight: Around 10 oz per square yard
- Weave count: 16 by 16 threads per inch on many models
- Reinforcement: Double-stitched hems and reinforced edges
- Grommets: Brass or metal rings spaced every 18 to 24 inches
- Resistance: Waterproof, with UV, tear, abrasion, and mildew protection
Smaller options like a 10 ft x 20 ft white commercial tarp carry the same 20 mil thickness in a lighter overall package.
Why Thickness Alone Doesn’t Decide Quality
A 20 mil rating tells you the material is thick, but it says nothing about the rest of the build. Two tarps can both measure 20 mils and perform very differently. The weave count determines how densely the polyethylene fibers are packed, while GSM (grams per square meter) reflects material density. Higher numbers in both mean a tighter, sturdier fabric.
Seams and grommets matter just as much. A tarp with 20 mil material but weak stitching will rip at the edges long before the fabric fails. Look for double-stitched hems, reinforced corners, and rust-resistant grommets spaced close enough to distribute stress evenly.
Weight and flexibility are the flip side. A 20 mil tarp is noticeably heavier and stiffer than thinner options. Plan for stronger tie-downs, sturdier poles or frames, and two people to handle large sizes. If you’re covering a small backyard grill or a pile of firewood for a season, a lighter tarp might serve you just fine.
How to Choose the Right Tarp for the Job
Match the tarp’s thickness to the punishment it will take. For construction materials, heavy machinery, or long-term vehicle storage, 20 mil is the right call. For occasional weekend use, 10 to 12 mil usually handles the job with less bulk and easier handling.
Check the full spec sheet before buying. Compare weave count, GSM, grommet spacing, and seam construction, not just the mil number. Also measure your actual cover area—tarps are sold by finished size, so a “20 x 20” tarp measures a full 20 feet by 20 feet after hemming.
If you’re ready to buy, our roundup of the best 20 x 20 heavy duty tarps breaks down top picks by build quality and value. Thickness is only half the story; the right choice balances material, reinforcement, and price for your specific use.
One more note: all thickness ratings refer to the material itself, not the tarp’s finished edge. Hems and reinforced borders add bulk, but the advertised mil rating measures the flat fabric.
References & Sources
- Derflex. “What Does Mil Mean on a Tarp?” Explains mil as a unit of thickness equal to 0.001 inch.
- Derflex. “Tarp Thickness Guide.” Breaks down mil ratings and typical uses for each thickness level.
- BCP. “Tarp Thickness Mil Guide.” Details common specifications and construction features for heavy-duty tarps.
