How to Calculate Flatbed Tarp Size: Truck and Trailer Coverage Guide

Flatbed Tarp Formula

A flatbed tarp must cover the cargo completely and secure to the deck below the load line:

Tarp length = cargo length + (cargo height × 2) + (deck overlap × 2)
Tarp width  = deck width + (cargo height × 2) + (deck overlap × 2)

Deck overlap (how far the tarp extends under the deck edge or attaches to side rails): typically 1–2 ft per side.

Step 1 — Know Your Deck Dimensions

Standard US flatbed dimensions:

• 48 ft trailer: 48 ft deck × 8.5 ft wide (102 inches)
• 53 ft trailer: 53 ft deck × 8.5 ft wide
• Step deck (lowboy): Lower deck 35–37 ft × 8.5 ft
• Flatbed truck (single axle): 20–26 ft deck × 8 ft wide

Step 2 — Measure Your Cargo

You need:

• Cargo length — longest dimension of the load
• Cargo width — widest point of the load (may exceed deck width for wide loads)
• Cargo height — from deck surface to the top of the load

Example: Structural steel on a 48 ft deck

• Cargo length: 40 ft (shorter than full deck)
• Cargo width: 6 ft (narrower than deck)
• Cargo height: 4 ft

Step 3 — Calculate

Using 40 ft cargo, 4 ft high, 8.5 ft deck, 1.5 ft deck overlap:

Tarp length = 40 + (4 × 2) + (1.5 × 2) = 40 + 8 + 3 = 51 ft
Tarp width  = 8.5 + (4 × 2) + (1.5 × 2) = 8.5 + 8 + 3 = 19.5 ft
→ Need: 20 × 52 ft tarp
→ Nearest standard: none — order a 20 × 55 custom flatbed tarp

Standard Flatbed Tarp Sizes

Flatbed tarps are sold differently from general-purpose tarps. They come in standardized trucking sizes:

Note: Flatbed tarp widths are set for deck coverage, not cargo coverage. The width covers the cargo AND hangs over the side to the deck. For material specifications (why vinyl is required for flatbeds), see the Tarp Types Guide.

DOT Tarp Requirements for Flatbeds

FMCSA regulations require that cargo on flatbeds be covered when the cargo could:

• Blow off during transit (loose materials, lightweight items)
• Cause road hazards if dropped
• Be damaged by weather (machinery, electronics, food products)

Requirements:

• Tarp must cover the full top surface of the load
• Tarp must be secured on all sides — no gaps at edges
• Metal banding alone is not sufficient for lightweight cargo

For construction debris, aggregate, or sand: State laws vary. Most states require full tarping of dump and end-dump trailers. Check state DOT requirements for your route.

Multiple Tarps for Long Loads

For loads exceeding the length of one standard tarp:

• Overlap tarps a minimum of 24 inches (2 ft) at the seam
• Front tarp overlaps rear tarp (like shingles) so rain runs off without entering the seam
• Secure each tarp independently with straps or side curtain hooks

Use the Tarp Size Calculator — select 3D Object Cover, enter cargo dimensions and deck width as object width.

See also: Tarp Size Formula and Standard Tarp Sizes Guide.