4 Mil vs. 8 Mil Poly Tarps: What Mil Means, Which Color to Buy, and a Size Chart
A tarp seems simple until you buy the wrong one. Too thin and it shreds in the first windy week. Too heavy and you have paid for more tarp than the job needed. The biggest difference between tarps is thickness, measured in mil. This guide explains what 4 mil and 8 mil mean, which jobs each one suits, how to pick a size, and when you actually need poly sheeting instead of a tarp.
What "mil" means
A mil is one thousandth of an inch. It is the standard way to describe the thickness of poly tarps and plastic sheeting. A higher number means a thicker, heavier material. Thickness is not the only thing that matters, since weave and coating play a part too, but it is the quickest way to compare tarps side by side.
4 mil poly tarps: the everyday option
Our 4 mil tarps are woven poly with a double laminated coating, a rope-reinforced hem, heat-sealed seams and grommets every 3 feet. They come in blue, brown and green.
A 4 mil tarp is a good fit when:
- You need a cover for a few days or weeks, not a full season
- You are covering lumber, tools or materials on site overnight
- You want a ground cover or a quick rain cover
- You are protecting a truck bed load for a short haul
- You want something light and easy for one person to handle
Because they are lighter, 4 mil tarps are also cheaper, which matters when you are buying several at once. Sizes on our site run from 5' x 7' up to 20' x 30' in blue and up to 40' x 60' in brown and green.
8 mil heavy-duty tarps: for longer exposure and rough use
Our heavy-duty tarps are 8 mil, made from 100% virgin polyethylene with a 10 x 14 weave count. They are listed as waterproof and UV resistant. Choose from green/black or silver/black.
Step up to 8 mil when:
- The tarp will stay outside for weeks or months
- It will be exposed to strong sun, wind or snow load
- You are covering equipment, machinery or a roof opening
- The tarp will be dragged, re-tied or moved often
- Replacing a torn tarp would cost you more than the upgrade
The heavy-duty line goes from 6' x 8' up to 100' x 100' in silver/black, so it also covers big jobs like whole roof sections or large material yards.
4 mil vs. 8 mil at a glance
- Weight and handling: 4 mil is lighter and easier to fold and carry. 8 mil is heavier and stiffer.
- Durability: 8 mil is the better choice for long-term outdoor use and rough handling.
- Cost: 4 mil costs less. For example, an 8' x 10' blue 4 mil tarp is $10.00, and a 20' x 30' is $40.00. A 20' x 30' green/black 8 mil tarp is $70.00. Check product pages for current prices.
- Best for: 4 mil for short-term covers and general use. 8 mil for long-term covers, equipment and harsh weather.
Which color tarp should you buy?
On our tarps, color does not change the thickness: all of our blue, brown and green tarps are 4 mil, and both two-tone tarps are 8 mil. So pick thickness first, then choose a color for the job:
- Blue is the classic, easy-to-spot general-purpose tarp.
- Brown and green blend in better outdoors, which some customers prefer for yards, farms, firewood and landscaping.
- Silver/black and green/black are our 8 mil heavy duty tarps. Light-colored surfaces generally reflect more sunlight than dark ones, which is one reason silver tarps are popular for covering equipment and materials left in the sun.
Silver/black vs. blue comes down to the job: a blue 4 mil tarp costs less and works well for short-term covers, while the silver/black 8 mil tarp is the heavier option for long-term outdoor use.
Tarp size chart
These are the sizes currently listed on our site. Check each product page for availability and current prices.
| Tarp | Sizes offered |
|---|---|
| Blue 4 mil | 5' x 7', 6' x 8', 8' x 10', 8' x 12', 8' x 15', 9' x 12', 10' x 10', 10' x 12', 10' x 15', 10' x 16', 10' x 18', 10' x 20', 10' x 22', 12' x 12', 12' x 14', 12' x 16', 12' x 18', 12' x 20', 12' x 22', 12' x 25', 12' x 36', 15' x 20', 15' x 25', 15' x 30', 16' x 20', 18' x 20', 18' x 24', 20' x 20', 20' x 25', 20' x 30' |
| Brown 4 mil | 5' x 7', 6' x 8', 8' x 10', 8' x 15', 9' x 12', 10' x 12', 10' x 15', 10' x 18', 10' x 20', 12' x 12', 12' x 16', 12' x 20', 12' x 25', 15' x 20', 15' x 30', 16' x 20', 18' x 24', 20' x 20', 20' x 25', 20' x 30', 20' x 40', 24' x 36', 30' x 40', 30' x 50'', 40' x 40', 40' x 60' |
| Green 4 mil | 5' x 7', 6' x 8', 8' x 10', 8' x 12', 8' x 15', 9' x 12', 10' x 10', 10' x 12', 10' x 15', 10' x 16', 10' x 20', 12' x 12', 12' x 14', 12' x 16', 12' x 20', 12' x 25', 15' x 20', 15' x 30', 16' x 20', 18' x 24', 20' x 20', 20' x 25', 20' x 30', 20' x 40', 24' x 36', 30' x 40', 30' x 50'', 30' x 60', 40' x 40', 40' x 60' |
| Green/black 8 mil | 8' x 10', 9' x 12', 10' x 12', 10' x 15', 10' x 20', 12' x 16', 12' x 20', 12' x 22', 12' x 25', 15' x 25', 15' x 30', 16' x 20', 18' x 24', 20' x 20', 20' x 25', 20' x 30', 20' x 35', 20' x 40', 25' x 40', 30' x 40', 30' x 50'', 30' x 60', 40' x 40', 40' x 60' |
| Silver/black 8 mil | 6' x 8', 8' x 10', 9' x 12', 10' x 10', 10' x 12', 10' x 15', 10' x 20', 12' x 16', 12' x 20', 12' x 25', 15' x 20', 16' x 20', 18' x 24', 20' x 20', 20' x 30', 20' x 40', 25' x 40', 30' x 40', 30' x 50', 30' x 60', 40' x 40', 40' x 60', 50' x 100', 100' x 100' |
How to pick the right size
Measure the item or area you want to cover, then add extra on every side so the tarp can wrap down and be tied off. A tarp that only just covers the top will let wind get underneath it. As a rule of thumb, add enough to reach your tie-down points comfortably. If you are between two sizes, go with the larger one.
Also keep in mind that finished tarp sizes can run slightly smaller than the listed cut size once hems are folded and sealed, which is common across the industry. If an exact fit matters, size up.
Tarp or poly sheeting?
Tarps and plastic sheeting are not the same thing. Tarps are woven, hemmed and fitted with grommets so you can tie them down. Poly sheeting comes on a roll, has no grommets and is meant to be cut to length. Use sheeting for:
- Dust barriers and containment during demolition or renovation
- Covering floors and furniture while painting
- Covering freshly poured or painted concrete
- Enclosing work areas during abatement
We carry clear poly sheeting in 2, 4, 6 and 10 mil rolls, black 6 mil sheeting, and fire retardant 6 mil sheeting for jobs that call for FR plastic. If you are protecting floors, a reusable canvas drop cloth is another option. See them all in our floor protection collection.
Care tips that make any tarp last longer
- Tie down at every grommet you can, so the load is spread out and wind cannot catch one corner
- Avoid sharp edges, or pad them, since corners on lumber and metal are where tears start
- Do not let water pool on top; pitch the tarp so rain runs off
- Let a wet tarp dry before folding and storing it
The bottom line
For short-term covers and general use around the home, yard, shop or job site, a 4 mil tarp is usually all you need. For anything that stays outside for a long time, faces rough weather or protects expensive equipment, spend a little more on 8 mil. And when you need a dust barrier or floor cover rather than a tie-down cover, reach for poly sheeting.
Browse every size and color in our poly tarps collection, or contact us for help choosing a tarp or for bulk quantities.