How it works
The calculator uses the common cargo securement rule of thumb based on working load limits:
Aggregate WLL needed = 50% × cargo weight
Effective WLL per strap = WLL (over the load) or WLL ÷ 2 (attached to the load)
Straps needed = aggregate needed ÷ effective WLL, rounded up, at least 2
WLL ≈ break strength ÷ 3 (web straps)
The 50% figure assumes friction and the cargo’s weight help hold it. Under hard braking a load pushes forward with close to its own weight, which is why blocking against a headboard or bulkhead is always a good idea.
Worked example
A 5,000 lb compact tractor, straps with a 1,000 lb WLL (3,000 lb break strength).
- Aggregate WLL needed: 5,000 × 0.5 = 2,500 lb
- Over the top (indirect): 2,500 ÷ 1,000 → 3 straps
- Hooked to the tractor’s tie-down points (direct): each counts 500 lb → 5 straps; in practice, use four corners plus one, or heavier chains.
Minimum straps by cargo weight
Indirect tie-downs (over the load). Double the count, roughly, for direct tie-downs.
| Cargo | 500 lb WLL | 1,000 lb WLL | 1,667 lb WLL | 3,333 lb WLL |
|---|---|---|---|---|
| 1,000 lb | 2 | 2 | 2 | 2 |
| 2,500 lb | 3 | 2 | 2 | 2 |
| 5,000 lb | 5 | 3 | 2 | 2 |
| 7,500 lb | 8 | 4 | 3 | 2 |
| 10,000 lb | 10 | 5 | 3 | 2 |
Placing tie-downs
Use at least one pair of straps pulling forward and one pulling back, at angles of 30–60° from the deck so they resist movement in every direction. On machines, use the manufacturer’s tie-down points. Lower buckets and attachments to the deck, and secure them separately. Re-check tension after the first few miles, since loads settle.
Before strapping, make sure the load fits the trailer’s cargo capacityand sits slightly ahead of the axle (see the load balance calculator).
Common mistakes
- Using break strength as the rating. A “3,000 lb” strap is often a 1,000 lb WLL strap.
- The weakest link. A strap’s WLL is limited by its hooks and the anchor point it’s attached to.
- All straps pulling the same way. Cargo needs restraint forward, back and sideways.
- Sharp edges. Use edge protectors; a cut strap has almost no strength.