Product Knowledge · 12 min read · Published November 2026
Quick answer
18 oz is the working standard for most US hay operations — it survives four to six years of sun in the Midwest and holds up to wind on a standard 20x24 or 24x27 tarp. 12 oz is for temporary cover, one season, light duty. 24 oz is for permanent storage in the Sun Belt (Texas, Florida, Arizona) or for round bales stacked three high where edge abrasion is the real failure mode.
Note on units: US hay tarps are sold by oz per square yard, not GSM. 18 oz equals roughly 610 g/m². This guide uses oz throughout because that is what your supplier's quote will be compared against.
A hay operation in central Nebraska bought 40 tarps at 14 oz because the price was 22% below the 18 oz quote. Two summers later, 31 of them had UV cracks along the fold lines and the edges had gone brittle enough to tear by hand. He replaced the whole set — and paid for 18 oz anyway, plus a season of ruined hay.
That story is not unusual, and it is not about a bad supplier. It is about buying a weight that was correct for a different scenario. Hay tarps fail in four specific ways, and each weight class handles a different subset of them. Choose the wrong one and it does not matter how good the fabric is.
Before comparing weights, it helps to know what you are buying protection against. Four failure modes account for almost every hay tarp replacement, and they do not rank the same way in every climate.
| Failure mode | Where it starts | Weight class that survives it |
|---|---|---|
| UV embrittlement | Along fold lines and at the top surface. The plasticiser migrates out, the PVC loses flexibility, and the first cold snap cracks it. | 18 oz in the Midwest. 24 oz for the Sun Belt, where UV dose is roughly 1.6x higher. |
| Edge abrasion | Where the tarp is pulled over bale edges, tied to equipment, or dragged during removal. The coating wears through and the scrim shows. | 24 oz, or 18 oz with reinforced hem and webbing at the corners. |
| Wind loading | Grommets pull out first, then the hem tears free. A larger tarp catches more wind — a 24x27 fails at a lower gust than a 16x20 of the same weight. | Weight helps, but spacing and hem depth matter more. See below. |
| Moisture wicking | Water travels along the yarn inside the cloth, then drips onto the bales from the underside. Not visible from outside. | No weight solves this. It requires anti-wicking treatment on the base cloth. |
Note the pattern: three of the four failure modes scale with weight, and one does not scale with anything you can see. That last one is why a buyer can do everything right on weight and still lose hay.
Here is what each class actually delivers. The GSM column is for cross-referencing with an Asian supplier's quotation; the oz column is what you will see on a US product listing.
| Specification | 12 oz ≈ 407 g/m² |
18 oz ≈ 610 g/m² |
24 oz ≈ 814 g/m² |
|---|---|---|---|
| Base cloth | 500D × 500D | 1000D × 1000D | 1000D × 1300D |
| Expected outdoor life Midwest (UV index moderate) |
1–2 seasons | 4–6 years | 8–10 years |
| Expected outdoor life Sun Belt (TX, FL, AZ) |
Under 1 season | 2–3 years | 5–7 years |
| Handling | One person, easy | Two people on larger sizes | Two to three people, or equipment |
| Repair | Rarely worth it | Patch kits work well | Worth welding, holds up |
| Cost per season indexed, 18 oz = 1.00 |
2.2–2.8× | 1.00 | 0.65–0.80× |
That last row is the one worth staring at. 12 oz is not cheap — it is the most expensive option per season of use, because you buy it two to three times in the period one 18 oz tarp would have covered. It only makes economic sense when the cover is genuinely temporary or when the tarp is expected to be destroyed by handling rather than by sun.
Why nobody quotes 24 oz first
A 24 oz hay tarp weighs about 45% more than 18 oz and costs proportionally more. Sellers rarely lead with it because it looks expensive on the invoice. But in the Sun Belt, where a 18 oz tarp lasts three years instead of six, the 24 oz is the cheaper purchase over any horizon longer than four years — and the labour saved on re-covering is worth more than the price difference for most operations running 100+ bales.
The weight decision is determined by four things about your operation, none of which is the quoted price.
| Your situation | Recommended | Why |
|---|---|---|
| Tarp covers hay for a few weeks, then stored indoors | 12 oz | Low UV dose, and the tarp will outlive its use. Paying for 18 oz is wasted. |
| Standard Midwest operation, tarps on year-round, replaced on a cycle | 18 oz | The default for good reason. Four to six years is long enough that the capital cost amortises well. |
| Texas, Florida, Arizona, or anywhere with intense summer sun | 24 oz | 18 oz degrades in three years there. The weight premium pays back by year three and keeps paying. |
| Round bales stacked three high, tarp pulled over edges repeatedly | 24 oz, or 18 oz with reinforced corners | Abrasion, not UV, is the limiting factor here. Reinforced hem and webbing at contact points buys most of the benefit. |
| Very large tarp (24x27 and up) in a windy location | 18 oz minimum + tight grommet spacing | Wind load rises with area, not with weight. Grommets every 24 inches beat a heavier fabric with grommets every 36. |
These are composite scenarios built from how hay and cattle operations actually buy tarps. The first two are the common ways money is lost; the third is the decision process that avoids both.
Scenario 1 — Nebraska, 40 tarps at 14 oz
A cow-calf operation with 600 head bought 40 tarps at 14 oz because the quote was 22% below the 18 oz option. The tarps were specified correctly in every other respect: right dimensions (24x27), good grommet spacing, proper hem. After two summers, 31 showed UV cracking along the fold lines and the edges had gone brittle. Result: the full set was replaced at year three. The 22% saved on the first purchase was spent roughly 1.8 times over across the replacement purchase and the hay that spoiled in the failed tarps.
Scenario 2 — Florida, 24 oz bought but water still got in
A horse operation near Ocala did the right thing on weight — 24 oz, correctly sized, from a reputable importer. The hay still got wet in the second season, but not from above. Water was travelling along the yarn inside the fabric and dripping from the underside onto the bales, visible only when a tarp was lifted. The fabric was a non-anti-wicking construction. Result: weight was never the problem. The operation paid for the correct gauge and still lost hay, because the failure mode it hit was the one that no weight class addresses.
Scenario 3 — Kansas, staged replacement instead of a full buy
A 1,200-head operation needed to replace 60 tarps but did not want to spend the full amount in one year. Instead of splitting the purchase across weights, the operator split it across function: 24 oz for the 20 tarps covering round bales stacked three high at the main yard (where abrasion and sun both bite), and 18 oz for the 40 tarps on square bales stored under partial shade on the north side of a windbreak. Both orders specified anti-wicking base cloth, 24-inch grommet spacing, and reinforced corners. Result: the same budget bought appropriate protection everywhere instead of uniform protection that was wrong in half the yard. The 24 oz units are on track for 9+ years; the 18 oz units sit at a realistic 5, which is correct for shaded storage.
Whatever weight you choose, four specification lines determine whether what arrives matches what you agreed. Without them, "18 oz" is a number a supplier can meet in several different ways — some of which fail in year two.
Pro tip: ask for the roll, not just the tarp
If you are covering more than about 20,000 sq ft of hay, buying finished tarps is often the more expensive route. A standard 16x20 ft tarp is 320 sq ft. A 100-metre roll of 5.0 m wide 18 oz fabric yields roughly 16 of them, and a roll ships more cheaply per square foot than 16 folded tarps because it is dense and has no air. If you have the means to cut and hem — or a local shop that will — asking a supplier for roll goods priced per square foot rather than finished tarps commonly changes the delivered cost by 15 to 25%. Ask for the quote both ways before deciding.
Usually not for year-round outdoor storage. Texas UV dose runs roughly 1.6 times the Midwest, which cuts an 18 oz tarp's realistic life from four to six years down to two to three. If the tarp is permanent cover, 24 oz pays back by year three. If it is seasonal and stored under cover half the year, 18 oz remains reasonable.
18 oz per square yard is approximately 610 g/m². The conversion factor is 33.9: one ounce per square yard equals 33.906 grams per square metre. When you compare a US product listing at 18 oz with an Asian quotation at 610 g/m², they are the same specification — but confirm the country of the ounce, because some suppliers quote oz per square metre, which is a different and much lighter number.
For short-term emergency cover, yes. For storage over a season, no. Woven polyethylene tarps breathe less predictably, degrade faster under UV, and are usually much lighter — a typical hardware-store poly tarp runs well under 6 mil. They also tend to trap condensation against the bale in a way that a coated fabric with anti-wicking treatment does not.
Every 24 inches along all edges is the US standard. On a 24x27 tarp that is roughly 46 grommets. Spacing at 36 inches is common on cheaper tarps and is the single most common cause of edge failure in wind — the fabric between grommets flutters, fatigues, and tears.
Less than most buyers expect. The UV stabiliser package matters far more than the pigment. However, lighter colours do run cooler, which slows plasticiser migration slightly. A black tarp in full Arizona sun will not outlast a white one of the same specification, but the difference is months, not years — the plasticiser and coating weight are the real variables.
You cannot tell by looking. The field test: cut a one-inch strip, stand it vertically with the bottom edge in a quarter inch of water, and watch. Treated fabric resists water climbing the yarn for hours; untreated fabric shows a visible dark line climbing within ten to fifteen minutes. Do this on a sample before you place the order, not on the tarp after it fails.
Below roughly 20,000 sq ft of coverage, finished tarps are simpler and the price difference is small. Above that, roll goods priced per square foot are usually 15 to 25% cheaper delivered, provided you have cutting and hemming capability. Ask for both quotes — the comparison itself tells you whether your supplier is pricing rolls competitively or padding them.
Cover the stack with at least 12 inches of overhang on every side so water sheds clear of the bottom bales, then size up one step. Standard sizes that cover most US operations are 16x20 ft for small stacks, 20x24 ft for a single row of round bales, and 24x27 ft for stacked or long rows. A tarp that only just covers the stack will wick at the bottom edge.
Sourcing hay tarps or roll goods at 12, 18 or 24 oz? Tell us the weight class, the tarp dimensions you need (or the roll width you cut to), how many bales you are covering, and whether the tarps stay out year-round or come in for the winter. We will come back with the base cloth and coating weight stated separately, the plasticiser type, and a price for both finished tarps and roll goods per square foot so you can compare the two routes properly. We run usable widths from 2.0 m to 5.0 m — 6.6 to 16.4 ft — which means most US tarp sizes can be cut without a seam down the middle.
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