Mil measures tarp thickness in thousandths of an inch, so 20 mil is 0.020 inches thick, and a heavy-duty starting range is roughly 12–16 mil.
Buying a heavy-duty tarp without understanding mil is how people end up with a flimsy sheet that shreds in the first windstorm. The number on the package tells you only how thick the material is—it does not guarantee strength. Here is what the numbers actually mean and how to match them to your job.
What Is a Mil on a Tarp?
A mil is a unit of thickness equal to one-thousandth of an inch (0.001 inch). Ten mil equals 0.010 inches; twenty mil equals 0.020 inches. It is not a millimeter, though the names sound similar.
For quick reference: 1 mil ≈ 0.0254 mm, 10 mil ≈ 0.254 mm, and 20 mil ≈ 0.508 mm. That is roughly half a millimeter at the heavy end—thin, but engineered for toughness rather than cushion.
Derflex’s heavy-duty tarp thickness guide groups common ratings into practical bands: 5–8 mil light duty, 10–12 mil medium to entry heavy-duty, 12–16 mil heavy-duty, and 20+ mil super heavy-duty / industrial.
What Thickness Do You Need for Heavy-Duty Use?
For construction sites, equipment covers, and commercial outdoor exposure, most buyer guides point to 12–16 mil as the heavy-duty starting range, with 14–20 mil as a practical working band for demanding jobs. If the tarp must survive long-term industrial use, 20+ mil is the safer call.
Match the mil rating to the work:
- 5–8 mil: light duty—temporary shade, dust covers, short-term DIY projects.
- 10–12 mil: medium duty—camping gear, occasional outdoor storage, entry-level contractor work.
- 12–16 mil: heavy-duty—construction sites, machinery covers, transport protection.
- 20+ mil: industrial—long-term outdoor storage, trailer tarps, aggressive commercial exposure.
Before you settle on a number, consider the one factor that beats thickness: material quality.
Why Thickness Alone Doesn’t Determine Durability
A 16-mil tarp can outperform a 20-mil tarp if the materials and construction are better. The same mil rating performs differently depending on the material family—polyethylene (PE) versus PVC-coated polyester—plus the fabric’s GSM (grams per square meter), base weave, tear strength, seams, and edge reinforcement.
Derflex’s guidance also notes that thickness does not guarantee waterproof performance by itself; heavy-duty spec sheets you should check pair mil with GSM and waterproof requirements rather than relying on thickness alone.
If you are covering a tractor or a pile of lumber for months, a 14-mil PVC-coated polyester tarp with reinforced hems and rustproof grommets will generally hold up better than a thicker PE tarp with weak stitching. Read the full spec, not just the mil number.
For a dependable, tested option in the most common heavy-duty size, our roundup of the best 10 x 12 heavy duty tarp picks compares real-world durability across leading models.
How to Choose the Right Heavy-Duty Tarp
Start with the job, then match the mil, then verify the construction details.
- Decide the exposure. Permanent outdoor storage in sun and snow needs 20+ mil; a seasonal equipment cover can work at 12–16 mil.
- Check the material family. PE tarps are cheaper and fine for light work; PVC-coated polyester handles harsher conditions and longer lifespans.
- Look at tear strength and seams. Reinforced hems, double-stitched seams, and rustproof grommets matter more than one extra mil.
- Consider handling. Very thick tarps get heavy and stiff—folding, dragging, and securing them takes real effort. If you move the tarp often, a slightly thinner but well-made option may serve you better.
The most common mistake is treating mil as millimeters, which makes a 20-mil tarp look far thinner than it is. The second most common is buying on thickness alone and ignoring UV resistance, reinforcement, and the fabric type underneath the number.
References & Sources
- Derflex. “Heavy Duty Tarps Thickness Guide.” Defines mil measurement and application bands for tarp selection.
