Cargo Tie-Down Calculator (FMCSA Working Load Limit)

US cargo securement rules set general minimums for articles secured with tie-downs: enough tie-downs for its length, and enough combined working load limit (WLL) to hold at least half its weight. This calculator applies both rules from 49 CFR Part 393 and shows how many straps or chains of a given type you need.

How to use this tool

1. Enter the weight and length of the article, or of a group of articles secured together.
2. Tick the box if a headboard, bulkhead or other cargo blocks it from moving forward.
3. Pick the tie-down type, or choose Marked WLL and enter the rating on your straps or chains.
4. Choose how the tie-downs are attached and how many you plan to use.

Formula

Required aggregate WLL = ½ × cargo weight; tie-downs needed = max(length minimum, ⌈required WLL ÷ WLL counted per tie-down⌉)

A tie-down that runs over or around the cargo from one side of the vehicle to the other counts its full WLL; one attached directly to the cargo, or looped back to the same side, counts half. Unblocked articles need 1 tie-down if 5 ft or shorter and 1,100 lb or less, 2 if up to 10 ft, and 1 more for each further 10 ft or part of 10 ft. Blocked articles need 1 per 10 ft or part.

Example

A 12,000 lb crate 16 ft long, not blocked: the length rule needs 2 + 1 = 3 tie-downs, and the WLL rule needs 6,000 lb in total. Four-inch webbing has a default WLL of 4,000 lb, so two straps over the top would satisfy the WLL rule, but the length rule still requires three. Four straps give 16,000 lb of aggregate WLL and meet both rules.