Ratchet Strap Guide

Tie-Down Working Load Limit Calculator

Enter the cargo weight, how many straps or chains you are using, each one's working load limit and how they are routed. The calculator adds up the aggregate WLL the way 49 CFR 393.106(d) counts it, tells you whether it reaches half the cargo weight, works out the minimum number of tiedowns from 393.110 for the article's length, and shows the WLL you would need per strap to pass. It is for anyone strapping a load to a truck, trailer or flatbed. Every number is an estimate; the label on your strap and the current regulation govern. Everything runs in your browser; nothing is uploaded, stored or sent.

Units

WLL means working load limit, not break strength. If your strap only lists break strength, strap makers and the WSTDA treat WLL as one-third of it. Unmarked widths use the 49 CFR 393.108(b) table; 1 in and 1-1/2 in webbing has no default there.

Calculating...

How it works, line by line

The calculator applies three sections of the Federal Motor Carrier Safety Administration cargo securement rules, 49 CFR Part 393 Subpart I, as published at law.cornell.edu and read on 28 October 2026.

Step 1, the WLL of one tiedown (393.108). A tiedown's working load limit is the lowest WLL of any component in the assembly, including the ratchet or tensioner, or the WLL of the anchor point, whichever is less. If you enter a lower-rated hook, ratchet or anchor, the calculator uses that figure instead of the strap's. For unmarked synthetic webbing, 393.108(b) assigns 1,750 lb at 1-3/4 inch, 2,000 lb at 2 inch, 3,000 lb at 3 inch and 4,000 lb at 4 inch. Unmarked chain is treated as grade 30.

Step 2, the credit for each tiedown (393.106(d)). A tiedown attached from an anchor point on the vehicle to the cargo counts one-half of its WLL. A tiedown that passes over the cargo and comes back to the same side also counts one-half. A tiedown that passes over the cargo and is attached to the other side counts its full WLL. So credit per tiedown = WLL x 0.5 (direct or same side) or WLL x 1.0 (other side).

Step 3, the aggregate (393.106(d)). Aggregate WLL = number of tiedowns x credit per tiedown. It must be at least one-half of the weight of the article. Pass means aggregate >= cargo weight / 2. The "WLL needed per tiedown" line is cargo weight / 2 divided by (count x credit factor): the smallest rated strap that passes with your count and pattern. The "tiedowns needed" line is the same requirement divided by the credit of one of your straps, rounded up.

Step 4, the minimum count (393.110). For an article that is not blocked against forward movement: 5 ft or shorter and 1,100 lb or lighter needs 1 tiedown; 5 ft or shorter and heavier than 1,100 lb needs 2; longer than 5 ft up to 10 ft needs 2; longer than 10 ft needs 2 plus 1 for every additional 10 ft or fraction. An article blocked against forward movement by a headerboard, bulkhead, other cargo or stakes needs 1 tiedown per 10 ft or fraction. The calculator reports which clause applied.

What it does not cover

  • Mixed patterns. If some straps go direct and some go over the top to the other side, run the tool twice and add the two aggregates by hand.
  • Commodity-specific rules in 393.116 to 393.136 (logs, lumber, metal coils, paper rolls, concrete pipe, intermodal containers, vehicles, heavy machinery, boulders). Those add or replace the general rules.
  • Strap angle. Part 393 counts WLL by pattern, not angle. For the engineering view of how a flat strap loses clamping force, use the strap angle calculator.
  • Condition. 393.104 bars damaged or weakened tiedowns and requires edge protection where webbing would be cut or abraded. A frayed 2,000 lb strap is not a 2,000 lb strap.
  • Applicability. Part 393 binds commercial motor vehicles under 49 CFR 390.5. Private pickups and trailers fall under state unsecured-load laws, but the same math is the sensible standard.

Results are arithmetic on the numbers you type, not legal advice. Every output is an estimate; the label on your strap and the current regulation govern. This site has commercial relationships described on the disclosure page; no products are recommended inside this tool.

Data last verified 2026-10-28. Prices, hours and rules change; results are estimates from the formulas shown; confirm the working load limit on your strap label and the current regulation before you haul.

Sources

Related guides

Frequently asked questions

What does aggregate working load limit mean?

It is the sum of the working load limits of every tiedown holding an article, counted the way 49 CFR 393.106(d) says: half the WLL for each tiedown that goes from the vehicle straight to the cargo, or over the cargo and back to the same side, and the full WLL for each tiedown that goes over the cargo and attaches on the other side. The total must be at least half the weight of the article.

Why does a direct tiedown only count half?

Section 393.106(d) assigns one-half of the WLL to a tiedown attached from an anchor point on the vehicle to the cargo. A strap that goes over the top and attaches to the far side restrains the load from both sides at once, so the rule credits its full WLL.

My strap has no label. What WLL do I use?

Section 393.108(b) gives default values for unmarked synthetic webbing: 1,750 lb for 1-3/4 inch, 2,000 lb for 2 inch, 3,000 lb for 3 inch and 4,000 lb for 4 inch. Unmarked 1 inch and 1-1/2 inch webbing has no default in the table; use the marked value from the maker or treat the strap as unrated. Unmarked chain is treated as grade 30.

Do these rules apply to my pickup or utility trailer?

Part 393 applies to commercial motor vehicles as defined in 49 CFR 390.5 (10,001 lb GVWR or more in interstate commerce, among other triggers). Private pickups and trailers fall under state unsecured-load laws instead, such as Washington RCW 46.61.655, California Vehicle Code 23114 and Texas Transportation Code 725.021. The federal math is still the clearest rule of thumb for any load.

Is the WLL on a strap the same as its break strength?

No. Break strength is the force at which a new strap fails. The working load limit is the rated capacity, and for synthetic web tiedowns strap makers and the WSTDA describe it as one-third of break strength. A strap sold as 3,000 lb break strength is a 1,000 lb WLL strap. Use the WLL in this calculator, never the break strength.