Lumber tarps are wider and taller—built to cover full-height loads with long side drops and usually an end flap. Steel tarps are shorter and built for low, dense loads like coils and plate. The names describe traditional cargo, but the decision is really about drop: measure your load height, add both side drops to the width, and choose the smallest tarp that reaches below the rub rail.
On most 48 ft and 53 ft flatbeds the practical choice comes down to a handful of stock sizes. Getting it wrong in either direction is expensive: a tarp that is too short cannot be stretched to fit, and a tarp that is too large is heavy, hard to tension, and wears out faster from flapping.
Common stock sizes
Suppliers vary, but these configurations are widely stocked in the US. Treat them as orientation, then confirm finished dimensions with the manufacturer before ordering.
| Type | Common stock size (width × length) | Typical drop | Best fit |
|---|---|---|---|
| Steel tarp | 16 × 20 ft, 16 × 27 ft | About 3–4 ft per side on a 8 ft 6 in deck | Coils, plate, pipe, low machinery |
| Lumber tarp | 20 × 27 ft, 24 × 27 ft | About 6–8 ft per side | Full-height boxed freight, lumber, palletized loads |
| Machinery / three-piece set | Varies by supplier | Sized to the known profile | Repeated coverage of one shape |
Many operators carry a matched pair—two 16 × 27 ft steel tarps, or two 24 × 27 ft lumber tarps—and overlap them at mid-deck. Two lighter tarps are easier to lift and fold than one full-length sheet, and a damaged section is cheaper to replace.
How to choose between them
- Load height is the deciding factor. Under about 4 ft tall, a steel tarp usually covers it. Taller loads need the longer drops of a lumber tarp.
- Check the width arithmetic. Tarp width must equal load width plus left drop plus right drop. An 8 ft 6 in wide load with 8 ft sides needs about 24 ft of fabric across.
- Count the ends. Full-length tall loads benefit from a lumber tarp's end flap. Low loads can be closed with a small drop and the main sheet.
- Plan the tie-off. The drop must reach below the rub rail with enough fabric left to secure. A drop that ends at the rail edge cannot be tensioned.
- Weigh the handling cost. Bigger is not safer if you cannot lift and control it. Check the total weight before committing to the largest option.
Measure before you buy
Use the loaded profile, not the deck label. Measure the load width at its widest point, the height from deck to top, and the length that must be covered. Then compute the required width and length before looking at stock sizes:
- Required width = load width + 2 × side drop
- Required length = covered load length + front overlap + rear overlap
Our Flatbed Tarp Size Guide walks through the full measurement sequence with worked examples, and the Tarp Size Calculator can check whether a stock size fits your numbers.
Do not ignore handling weight
Fabric weight scales with area. At 18 oz/yd² (about 610 GSM), a 24 × 27 ft lumber tarp works out to roughly 90 lb of fabric before hems, D-rings, and reinforcement. Two people and a calm day are a sensible minimum for spreading a tarp that size. Use the Tarp Weight Calculator to check the number for your exact size and fabric.
Wind makes the decision for you
A large tarp becomes a sail the moment it leaves the folded stack. If you regularly work alone or in exposed locations, a matched pair of smaller tarps is usually the more practical answer than one maximum-size sheet.
Common mistakes
- Buying by cargo name instead of dimensions. A load of lumber that is only 3 ft high does not need lumber-tarp drops.
- Ignoring the drop on both sides. The side drop counts twice in the width calculation.
- Assuming 48 ft means 48 ft of coverage. The covered load length is often shorter; measure the freight.
- Choosing the biggest tarp “just in case.” Excess fabric flaps, chafes, and adds weight you pay for every trip.
- Forgetting the overlap. When running two tarps, the seam must face away from the expected airflow so wind cannot get under it.
Frequently asked questions
Can I use a steel tarp on a tall lumber load?
Only if the drops reach far enough down the load sides to tie off below the rub rail. A 16 ft wide steel tarp on an 8 ft 6 in wide load leaves under 4 ft per side, which is too short for most full-height freight. Measure the load first, then check whether the tarp width covers top plus both drops.
Is a lumber tarp always the safer choice because it is bigger?
No. Extra fabric that you cannot tension flaps in the wind, chafes through faster, and adds handling weight. A full-size 24 × 27 ft lumber tarp in coated fabric can weigh 90 lb or more before hardware. Match the drop to the load height and choose the smallest configuration that covers it properly.
What does the second number in a tarp size mean?
Flatbed tarp sizes are listed as width × length. A 16 × 27 steel tarp is 16 ft across the load and 27 ft along the deck. The width must equal load width plus both side drops; the length covers the load front-to-back plus end flaps or overlap.
Do I need an end flap?
End flaps on lumber tarps close the front face of a tall load against road spray and wind. They matter most on tall, full-length loads. For low steel loads the front is usually covered by the main sheet and a small drop, so a flap is less critical.
Are lumber and steel tarps made from different material?
Usually not the base fabric—most are 18 oz PVC-coated polyester. The difference is size and drop geometry. What does change by supplier is reinforcement: D-ring rows, hem construction, and abrasion pads. Compare the finished specification, not only the name.
How this guide was prepared
We separate geometry and unit conversions from product claims, use exact standards where available, and flag specifications that vary by manufacturer. See our editorial policy for the review process.