Four rules run through every guide below
The scenes differ, but the arithmetic does not. Whether you are covering a hay stack, a jon boat, or a flatbed load, four things decide whether the tarp fits.
1. Allowance is applied twice
A tarp extends in both directions. If you want 16 in past each end, you add 32 in to the length, not 16. This single mistake accounts for more short covers than any other. The same applies to side allowance and the width.
2. A draped object needs two full drops
Covering something with height is not a footprint problem. If the cover must reach the ground on both sides, add twice the object height to the matching dimension, on top of the allowance. A 6 ft wide machine standing 4 ft tall needs at least 6 + 4 + 4 = 14 ft of width before any working overlap.
3. Both dimensions must clear independently
Area is not a fit test. A 14 × 21 ft minimum does not fit a 16 × 20 ft tarp even though the tarp has more square footage. Rotating helps only when both rotated dimensions clear. Compare length to length and width to width, every time.
4. Labeled size is often not finished size
Many consumer tarps are sold by cut size, measured before hems and seams take material out of the finished panel. A tarp labeled 10 × 12 ft can arrive several inches short in both directions. Look for a stated finished size or a tolerance, and plan coverage from that number.
Round up, but have a plan for the excess
An oversized cover can be folded, tucked, and tensioned. An undersized one simply fails. But excess fabric still needs managing so it does not flap in wind, pool water in a low spot, or hang into wheels and walkways.
Which guide to open
If you are covering something with a simple rectangular footprint — a wood pile, a pallet, a stack of materials — the Tarp Sizing Guide covers the general method and is the right starting point. Go to a scene-specific guide when the object introduces geometry the general method does not handle: a pitched roof where slope length exceeds the building width, a boat with a curved beam and drainage requirements, a pool where the anchor line sits well outside the waterline, or equipment with attachments and contact points that increase the real profile.
For anything on a truck or trailer, use the truck tarp guides. Load geometry, drop requirements, and cargo-securement rules make those a separate problem from static storage.
Once you have a minimum size, the Tarp Size Calculator does the arithmetic and rounds to a common stock size, and the Tarp Weight Calculator tells you whether one person can still handle the result.