Tarp Size Formula: How to Calculate the Right Tarp Dimensions

Three Tarp Size Formulas

Tarp sizing depends on what you’re covering. There are three distinct calculation methods:

1. Flat Ground Cover

Use for: pools, ponds, patio furniture (flat), ground sheets, crop protection.

Tarp length = coverage length + (overhang × 2)
Tarp width  = coverage width  + (overhang × 2)

The overhang is the extra tarp beyond the edge on each side. Recommended: 2 ft (0.6 m) minimum. More overhang = better wind resistance and water runoff.

Example: 20 × 12 ft pool, 2 ft overhang:

Tarp length = 20 + (2 × 2) = 24 ft
Tarp width  = 12 + (2 × 2) = 16 ft
→ Need: 16 × 24 ft tarp
→ Standard match: 16 × 20 ft (fits width, slightly short on length) or 20 × 25 ft

2. Three-Dimensional Object Cover

Use for: woodpiles, outdoor equipment, furniture stacks, lumber piles.

Tarp length = object length + (height × 2) + (ground overlap × 2)
Tarp width  = object width  + (height × 2) + (ground overlap × 2)

The height × 2 accounts for the tarp draping down both ends/sides. The ground overlap × 2 is extra tarp on the ground per side for anchoring.

Example: Woodpile 8 ft long × 4 ft wide × 5 ft high, 1 ft ground overlap:

Tarp length = 8 + (5 × 2) + (1 × 2) = 8 + 10 + 2 = 20 ft
Tarp width  = 4 + (5 × 2) + (1 × 2) = 4 + 10 + 2 = 16 ft
→ Need: 16 × 20 ft tarp — standard size available

3. Hay / Silage Stack Cover

Same formula as 3D object, but with larger recommended ground overlap (2–3 ft) for anchoring under the bales:

Tarp length = stack length + (height × 2) + (tuck-under × 2)
Tarp width  = stack width  + (height × 2) + (tuck-under × 2)

Standard tuck-under: 2 ft on each side. Tuck the extra tarp under the bottom row of bales — this is the primary anchor method for hay tarps without stakes. For step-by-step hay tarp calculation with stack shape variations, see How to Calculate Hay Tarp Size.

Example: 30 × 20 ft hay stack, 10 ft high, 2 ft tuck-under:

Tarp length = 30 + (10 × 2) + (2 × 2) = 30 + 20 + 4 = 54 ft
Tarp width  = 20 + (10 × 2) + (2 × 2) = 20 + 20 + 4 = 44 ft
→ Need: 44 × 54 ft tarp — no exact standard; use two 25 × 40 tarps overlapped

Variables Defined

Metric Formula (Metres)

Same formulas apply with metres:

Flat: tarp_m = coverage_m + (overhang_m × 2)   [each dimension]
3D:  tarp_m = object_m + (height_m × 2) + (overlap_m × 2)

1 foot = 0.3048 metres. A 20 × 30 ft tarp = 6.1 × 9.1 metres.

Standard Tarp Sizes (US, in feet)

When needed dimensions fall between standard sizes, always round up to the next available size. Never round down — the tarp will not cover adequately. See the Standard Tarp Sizes Guide for the full list of available sizes by category.

Use the Tarp Size Calculator — select your use case and enter dimensions.

See also: Standard Tarp Sizes Guide and How to Calculate Hay Tarp Size.