About the Cargo Tie-Down Calculator
This cargo tie-down calculator applies the two general US cargo securement tests that every flatbed load has to pass. First, the aggregate working load limit (WLL) of the tiedowns must be at least half the weight of the article (49 CFR 393.106(d)). Second, there is a minimum number of tiedowns based on the article’s length, its weight and whether it is blocked against forward movement by a headerboard, bulkhead or other cargo (49 CFR 393.110). The answer is whichever count is higher.
Pick the strap or chain you are using and how it is attached. A tiedown that runs from the trailer, over the cargo and down to the other side counts at its full WLL; one that is hooked directly to the cargo, or goes over the cargo and back to the same side, counts at only half its WLL. If the tiedown is marked with a WLL, choose “Marked WLL” and enter that figure; otherwise the tool uses the default values from the tables in 49 CFR 393.108 (for example 3,000 lb for a 3-inch web strap and 6,600 lb for 3/8-inch grade 70 chain).
It is meant for owner-operators, flatbed drivers, shippers and safety managers checking a load plan. It covers the general rules only: logs, metal coils, paper rolls, concrete pipe, intermodal containers, vehicles, heavy machinery, boulders and other commodities in 49 CFR 393.116–393.136 have additional or different requirements, and the minimum-count rule does not apply to special-purpose vehicles carrying items that must be fastened by special methods. Figures reflect the eCFR text current in October 2026.
With the default inputs, the minimum tiedowns required is 3. Change any value above to recalculate instantly.
How to use the cargo tie-down calculator
- 1Enter the weight and length of the article (or group of articles secured together).
- 2Say whether it is blocked against forward movement by a headerboard, bulkhead or other secured cargo.
- 3Choose your strap or chain, or enter the WLL marked on it.
- 4Choose how the tiedowns are attached — over the cargo side to side, or hooked directly to the cargo.
- 5Read the minimum tiedowns required, and optionally enter how many you plan to use to check both tests.
Formula and method
Under 49 CFR 393.106(d) the sum of the tiedowns’ working load limits must be at least half the weight of the cargo. Each tiedown is credited with its full WLL (k = 1) when it goes from an anchor on one side of the vehicle, over or around the cargo, to the other side; it is credited with half its WLL (k = 0.5) when it goes from the vehicle to an anchor point on the cargo, or over the cargo and back to the same side.
Under 49 CFR 393.110, an article that is not blocked against forward movement needs one tiedown if it is 5 ft or shorter and 1,100 lb or lighter; two if it is 5 ft or shorter but heavier, or between 5 and 10 ft long; and for articles longer than 10 ft, two tiedowns plus one more for every additional 10 ft or fraction. An article blocked by a headerboard, bulkhead or other secured cargo needs one tiedown per 10 ft of length or fraction. The calculator reports the larger of the two counts. Unmarked tiedowns use the default WLL tables in 393.108; the WLL of an assembly is that of its weakest component or anchor point.
- W
- Weight of the article or group of articles (lb)
- WLL
- Working load limit of one tiedown (marked, or from the 393.108 tables)
- k
- Credit factor: 1 for side-to-side over the cargo, 0.5 for direct or same-side attachment
- n_length
- Minimum count from the length/weight rule in 393.110
Worked examples
12,000 lb, 16 ft load with 3-inch straps over the top
Half of 12,000 lb is 6,000 lb of aggregate WLL, which two 3,000 lb straps over the top would cover. But an unblocked 16 ft article needs two tiedowns for the first 10 ft plus one for the remaining 6 ft, so 3 are required. Four planned straps give 12,000 lb of aggregate WLL and pass both tests.
1,800 lb crate, 4 ft long, strapped to its own anchor points
The crate is under 5 ft but heavier than 1,100 lb, so at least two tiedowns are required. A 2-inch strap hooked directly to the crate only counts for half its 2,000 lb WLL (1,000 lb); one would satisfy the 900 lb aggregate requirement, but the length/weight rule sets the minimum at 2.
30,000 lb machine, 12 ft, blocked, 3/8 in grade 70 chain
Because the article is blocked, the length rule needs only one tiedown per 10 ft or fraction — 2 for 12 ft. Strength governs instead: 15,000 lb ÷ 6,600 lb per chain = 2.27, rounded up to 3 chains. Four chains provide 26,400 lb. (Heavy machinery over 10,000 lb also has commodity-specific rules in 393.130.)
40,000 lb, 20 ft load chained directly to the cargo with 5/16 in grade 70
Attached directly to the cargo, each 4,700 lb chain is credited with only 2,350 lb. Reaching 20,000 lb of aggregate WLL takes 20,000 ÷ 2,350 = 8.5, rounded up to 9 chains — far more than the 3 the 20 ft length rule requires, so 8 planned chains fall short.
Frequently asked questions
How many tie-downs do I need on a flatbed load?+
Under 49 CFR 393.110 an unblocked article needs 1 tiedown if it is 5 ft or shorter and 1,100 lb or less, 2 if it is heavier or up to 10 ft long, and 2 plus 1 for every extra 10 ft (or fraction) beyond 10 ft. You also need enough tiedowns for their combined WLL to reach half the cargo weight, so use whichever count is higher.
What is the aggregate working load limit rule?+
The working load limits of all tiedowns securing an article must add up to at least 50% of the article’s weight (49 CFR 393.106(d)). A tiedown attached directly to the cargo, or passing over it and returning to the same side, counts at half its WLL; one passing over the cargo from one side of the vehicle to the other counts at its full WLL.
What WLL do I use if my strap or chain is not marked?+
Use the default tables in 49 CFR 393.108: for example 2,000 lb for 2-inch synthetic webbing, 3,000 lb for 3-inch and 4,000 lb for 4-inch. Unmarked welded chain is treated as grade 30 proof coil (1,900 lb at 5/16 in), and unmarked synthetic rope is treated as polypropylene.
Does blocking the cargo reduce the number of tiedowns?+
Yes. If an article is blocked against forward movement by a headerboard, bulkhead, other adequately secured cargo or another blocking method, it needs only one tiedown per 10 ft of length or fraction (49 CFR 393.110(c)). The aggregate WLL requirement still applies.
Is the WLL the same as the breaking strength?+
No. The working load limit is the maximum load a tiedown should carry in service and is normally a fraction of its breaking strength (often about one-third for web straps). Always use the WLL, and remember that the weakest part of the assembly — hook, ratchet, binder or anchor point — sets it.
Do these rules apply to coils, logs and vehicles?+
The general rules apply, but commodity-specific sections 393.116–393.136 add extra requirements for logs, dressed lumber, metal coils, paper rolls, concrete pipe, intermodal containers, automobiles and light trucks, heavy vehicles and machinery, flattened cars, roll-on/roll-off containers and boulders. Where those rules differ, they take precedence.
Results are general estimates and not legal advice. Laws vary by jurisdiction — consult a qualified attorney.