Picking a 20 x 20 tarp comes down to matching material and thickness to your use — 5–8 mil polyethylene for temporary cover, 8–12 mil for general outdoor protection, and 14 mil and up for repeated or industrial work.
For the full breakdown, see our best 20 x 20 Tarp guide.
A tarp that looks perfect on the listing page can shred at the first tie point if it’s too thin for the job. The three numbers that decide whether a 20 x 20 tarp lasts one season or five — size, material, and thickness — are also the three most misread. Get those right and you sidestep the wind-tear failure most buyers hit in month two.
What “20 x 20” Actually Means Before You Buy
A 20 x 20 tarp is usually a nominal 20-foot by 20-foot sheet — but the finished size can be smaller once hems and seams are factored in, so it pays to check which figure the listing is quoting. Some products list cut size (the flat sheet before finishing) while others list finished size (what you actually unfold). The difference matters when you’re covering something with a precise footprint.
Cut size is the raw material dimension; finished size is what remains after edges are hemmed and reinforced. For loose covering — firewood, a woodpile, a trailer load — a slightly smaller finished size rarely matters. For anything measured to fit, verify the finished figure first. If the listing doesn’t separate the two, treat the stated number as nominal and allow a few inches of slack.
Which Material Belongs On Your Job?
Polyethylene tarps handle most general outdoor coverage, while heavier vinyl or reinforced industrial tarps suit long-term exposure, abrasion, and high wind loads. Both materials appear throughout current 20 x 20 listings, and the right pick tracks your exposure length, not the price tag.
Polyethylene (often shortened to PE or “poly”) is the everyday choice: light, affordable, and fine for dust, short-term shelter, and seasonal covering. Heavy-duty vinyl is denser and resists abrasion and puncture better, which is why it shows up on machinery covers and industrial protection. The material also sets your handling experience — a heavy vinyl sheet is stiffer and harder to fold solo, while poly drapes and packs more easily.
Whichever material you land on, the same three checks decide quality for both:
- Reinforced corners and hemmed edges — the first places a tarp fails.
- UV resistance and waterproofing — the difference between one summer and several.
- Tear and rip resistance — weighed alongside fabric weight, not instead of it.
How Thickness (Mil) Changes Durability
Thickness is measured in mil, and higher mil generally means thicker, stronger, and heavier — but also less flexible and harder to manage. Current 20 x 20 offerings cluster around 5 mil, 12 mil, 16 mil, 18 mil, and 20 mil, each mapped to a different job.
A thickness guide from Derflex puts the ranges in plain terms: 3–6 mil covers light temporary protection, 8–12 mil handles general outdoor protection, 14–20 mil is heavy-duty, and 20 mil and above is industrial or severe-duty territory. That scales cleanly to real 20 x 20 products — a 5 mil poly for dust and short cover, a 12 mil for firewood or equipment, and a 16–20 mil for machinery, transport, or repeated outdoor use.
Here’s the part buyers skip: mil alone doesn’t tell you strength. Fabric weight and weave count do much of the work. A 20 mil tarp might list 11 oz/sq yd and a 16 x 16 weave, a medium-duty 11–12 mil sheet around 6 oz/sq yd, and a light-duty 5–6 mil option near 2.9 oz/sq yd. Grommet spacing matters too — current 20 x 20 tarps run about every 18 inches, 19.5 inches, or 36 inches, and closer spacing spreads wind load better across the tie points.
| Thickness Range | Typical Use | Common Material |
|---|---|---|
| 5–8 mil | Dust cover, short-term shelter | Polyethylene (PE) |
| 8–12 mil | Firewood, equipment, seasonal storage | Polyethylene (PE) |
| 12–14 mil | General outdoor, moderate wind | PE or reinforced |
| 16 mil | Super-heavy-duty outdoor use | Reinforced poly |
| 18 mil | Construction, transport protection | Heavy-duty fabric |
| 20 mil | Machinery, long-term exposure | Vinyl or reinforced |
| 20 mil+ | Industrial, abrasive, high-stress | Heavy vinyl, dense weave |
Thinner sheets fail fastest in wind because load concentrates at the tie points, and a 5 mil tarp is more likely to tear there than a 16 mil one. The Derflex tarp selection guide pairs these thickness bands with material and fabric weight so you’re comparing more than one number. For readers ready to move from spec sheet to purchase, these top-rated 20 x 20 tarps are tested and compared by use case.
Matching the Tarp to Wind and Long-Term Exposure
For wind-prone or long-term outdoor use, heavier fabric and closer grommet spacing beat a thin sheet every time — the failure mode is almost always a torn grommet, not a punctured panel. Before you tie anything down, check how the load distributes across your attachment points; hardware spacing varies widely by product, and a tarp rated for 50 mph gusts needs corners that can take the tension.
Two more compatibility checks save returns. A tarp built for equipment cover isn’t the same as one intended for awning coverage, sheltering, or machinery protection, so confirm the application matches. And for vehicle or industrial use, weigh the trade: thicker products protect better but deploy and secure harder, which matters if you set up and take down often.
Common mistakes, briefly: assuming all 20 x 20 tarps cover the same square footage, trusting mil as the sole quality signal, choosing a thin option for windy exposure, and neglecting UV resistance and edge reinforcement. Fix those four and you’ve fixed most of the failures buyers report.
FAQs
Is a 20 mil tarp too heavy for regular household use?
Often, yes. A 20 mil sheet is dense and stiff, which makes solo folding, dragging, and quick tie-downs harder. For occasional home jobs like covering firewood or a lawn pile, an 8–12 mil polyethylene tarp gives you enough protection with far less effort. Reserve 20 mil and above for machinery, transport, or repeated industrial exposure.
Does a higher mil number always mean a stronger tarp?
No. Mil measures thickness, not the total strength package. Fabric weight in oz/sq yd, weave count, seam reinforcement, and grommet spacing all shape how a tarp holds up under load. A thicker sheet with sparse grommets can fail sooner than a slightly thinner one with reinforced corners and hemmed edges.
How far apart should grommets be on a wind-exposed tarp?
Closer is better under wind load. Current 20 x 20 tarps list grommets roughly every 18 inches, 19.5 inches, or 36 inches, and the tighter spacings spread tension across more tie points. If you’re covering something in a gusty spot, favor the 18- to 19.5-inch spacing and use every grommet, not just the corners.
References & Sources
- Derflex. “Tarp Thickness Guide” Maps mil ranges to light, general, heavy-duty, and industrial protection levels.
- Derflex. “How To Choose Tarp GSM, Oz and Thickness” Explains how fabric weight and thickness work together.
- Derflex. “How To Choose a Tarpaulin: GSM, Thickness and Weight Guide” Supports material and use-matching guidance.
