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BuyCargo Securement Tiedown Calculator
How many straps or chains the load needs — and which of the two federal rules is the one you are failing
Securing a load is governed by two separate requirements that run at the same time. One is about strength: the tiedowns together have to carry at least half the weight of the article. The other is about count: the article has to have a minimum number of tiedowns on it based on how long it is, whatever they are rated at. People satisfy one and miss the other constantly, because they are different rules with different inputs and nothing on a strap tells you about either. This runs both, tells you which one is binding, and shows what changing the hardware or the way you route it would do.
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The gear that turns this from a guess into a number
Two of the three inputs above are measurements people eyeball: the weight of the article and its length. Both of them move the answer in steps, not smoothly — 1,100 lb is the line between one tiedown and two, and every 10 ft adds another one. The third thing worth having on the trailer is chocks, because 393.106(c)(1) requires anything likely to roll to be restrained by chocks, wedges or a cradle before tiedowns enter the conversation at all.
MaxxHaul 70472 Solid Rubber Wheel Chocks 2-Pack
- 393.106(c)(1) requires articles likely to roll to be restrained by chocks, wedges or a cradle
- The rule also says the restraint must not be able to work loose in transit
- Rubber grips a wood or steel deck rather than skating on it
TIPRE Digital Shipping Postal Scale 660 lb
- Weight is the input that decides one tiedown or two under 393.110(b)
- Aggregate WLL is a straight half of the weight — guess the weight, guess the requirement
- 660 lb capacity covers the crates, pallets and small machines that sit near the line
Sherline LM 2000 Trailer Tongue Weight Scale
- A load can be perfectly secured and still unstable if it sits in the wrong place
- Securement stops the article moving; tongue weight is what stops the trailer swaying
- Pairs with the TestTalkHQ trailer tongue weight calculator
Mechanix Wear The Original Hi-Viz Work Gloves
- Transport chain, binders and wire rope all punish bare hands
- Hi-viz matters when the load gets re-checked on a shoulder
- Enough feel left to run a ratchet and read a WLL tag
Klein Tools 60171 Anti-Fog Safety Glasses 2-Pack
- A lever binder coming off a tensioned chain is the classic way people get hurt
- Webbing under load stores energy and does not fail politely
- Anti-fog matters because securement checks happen in the weather
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Two rules, running at the same time
Almost every argument about whether a load is secured properly is really an argument about which rule somebody has in their head. There are two, they are independent, and both have to be satisfied.
Aggregate working load limit ≥ ½ × weight of the article (49 CFR 393.106(d))
Minimum number of tiedowns, set by length and — under 5 ft — weight (49 CFR 393.110)
The first is about strength. Add up what the tiedowns are rated to hold, counted the way the regulation counts them, and that total has to be at least half the weight of what you are holding down. The second is about count, and it does not care how strong anything is. A 24 ft beam needs four tiedowns whether it weighs 600 lb or 6,000 lb.
This is the failure people actually get written up for. One heavy chain on a long article is the classic case: the aggregate working load limit is comfortably over the requirement, and the load is still short by two tiedowns because 393.110(b)(3) asks for two in the first 10 ft and one more for every 10 ft after that. Strength does not buy you out of the count.
Why a strap over the top can be worth double — or not
This is the single most misread sentence in Subpart I, and it is worth quoting in full. 393.106(d) says the aggregate working load limit is the sum of:
| Clause | How the tiedown runs | Counts as |
|---|---|---|
| 393.106(d)(1) | From an anchor point on the vehicle to an anchor point on the article of cargo | One-half the WLL |
| 393.106(d)(2) | From a vehicle anchor, through / over / around the cargo, back to an anchor on the same side | One-half the WLL |
| 393.106(d)(3) | From a vehicle anchor, through / over / around the cargo, to an anchor on the other side | The full WLL |
The shop shorthand is “a strap over the load counts double.” That is only true for the third case — the tiedown has to reach right across and anchor on the far side. A strap thrown over a crate and ratcheted back down to a rail on the side it started from is the second case and counts half, exactly the same as a hook straight into a lifting eye on the cargo.
The free fix. Going from same-side to opposite-side routing doubles the aggregate working load limit of hardware you already own. On a 6,000 lb article needing 3,000 lb of aggregate, four 2 in straps run back to the same side give you 4,000 lb; the same four straps run across the deck give you 8,000 lb. Nothing was bought. The straps were simply routed the way the regulation counts in full.
The count rule, in the order it actually branches
393.110 splits first on whether the article is blocked against forward movement, then on length, and only then — below five feet — on weight.
| Situation | Clause | Minimum tiedowns |
|---|---|---|
| Not blocked forward, 5 ft or less and 1,100 lb or less | 393.110(b)(1) | 1 |
| Not blocked forward, 5 ft or less but over 1,100 lb | 393.110(b)(2)(i) | 2 |
| Not blocked forward, over 5 ft up to 10 ft, any weight | 393.110(b)(2)(ii) | 2 |
| Not blocked forward, over 10 ft | 393.110(b)(3) | 2, plus 1 for every 10 ft or part of 10 ft beyond the first 10 |
| Blocked or braced against forward movement | 393.110(c) | 1 for every 10 ft or part of 10 ft |
Worked: a 20 ft 6 in steel beam, not blocked forwardLength is over 10 ft, so 393.110(b)(3) applies: two tiedowns for the first 10 ft, then one more for every 10 ft or fraction thereof beyond it. Beyond the first 10 ft there is 10 ft 6 in left, which is one full 10 ft plus a fraction — so two more, not one.
Minimum: 4 tiedowns. Block the same beam against a headerboard and 393.110(c) gives you one per 10 ft or fraction, which for 20 ft 6 in is 3.
Minimum: 4 tiedowns. Block the same beam against a headerboard and 393.110(c) gives you one per 10 ft or fraction, which for 20 ft 6 in is 3.
“Or fraction thereof” always rounds up. Six inches over a 10 ft boundary is a whole extra tiedown. This is why the length measurement is worth taking rather than guessing — there is no rounding to the nearest anything.
Where the working load limit number comes from
393.108 sets out the order of precedence clearly. A manufacturer's marking on the hardware governs. Only where the tiedown is not marked do you fall back on the tables in the regulation — and those defaults are deliberately conservative.
| Chain size | Grade 30 proof coil | Grade 43 high test | Grade 70 transport | Grade 80 alloy | Grade 100 alloy |
|---|---|---|---|---|---|
| 7 mm (1/4 in) | 1,300 | 2,600 | 3,150 | 3,500 | 4,300 |
| 8 mm (5/16 in) | 1,900 | 3,900 | 4,700 | 4,500 | 5,700 |
| 10 mm (3/8 in) | 2,650 | 5,400 | 6,600 | 7,100 | 8,800 |
| 11 mm (7/16 in) | 3,700 | 7,200 | 8,750 | — | — |
| 13 mm (1/2 in) | 4,500 | 9,200 | 11,300 | 12,000 | 15,000 |
| 16 mm (5/8 in) | 6,900 | 13,000 | 15,800 | 18,100 | 22,600 |
Working load limits in pounds, from the tables to 393.108. Note the 5/16 in row: the table lists Grade 80 alloy below Grade 70 transport. That is what the regulation says, and the calculator reproduces it rather than quietly tidying it up. Note also that the 7/16 in row has no Grade 80 or Grade 100 entry at all.
| Synthetic webbing | WLL (lb) | Wire rope 6 × 37 FC | WLL (lb) |
|---|---|---|---|
| 1-3/4 in | 1,750 | 1/4 in | 1,400 |
| 2 in | 2,000 | 3/8 in | 3,000 |
| 3 in | 3,000 | 1/2 in | 5,300 |
| 4 in | 4,000 | 5/8 in | 8,300 |
Unmarked hardware defaults downward, hard. Unmarked welded steel chain is treated as Grade 30 proof coil — at 3/8 in that is 2,650 lb instead of the 6,600 lb a marked Grade 70 chain of the same size would carry. Unmarked synthetic cordage is treated as polypropylene, the weakest rope in the tables. Unmarked wire rope is treated as 6 × 37 fiber core. Buying marked hardware is not paperwork; it is more than double the credit on the same steel.
The weakest link is usually not the strap
393.108(a) is one sentence and it quietly reframes everything above: the working load limit of a tiedown is the lowest working load limit of any of its components, including the tensioner, or of the anchor points it is attached to, whichever is less.
A 4 in strap rated 4,000 lb running through a stake pocket rated 2,000 lb is a 2,000 lb tiedown. So is the same strap with a 3,300 lb ratchet on it, or a flat hook rated below the webbing, or a D-ring welded to a deck by somebody who did not look up a rating. Every one of those is a component in the assembly and the lowest number wins.
This is where paper securement and real securement diverge. The calculator above takes the weakest component as an input precisely because it is the number nobody has. If you have never established what the anchor points on your trailer are rated at, you do not actually know your aggregate working load limit — you know an upper bound on it.
393.104(c) closes the loop from the other end: the vehicle structure, deck, stakes, posts and mounting pockets themselves have to be strong enough to meet the 393.102 performance criteria, with no cracks, cuts or damage that reduce the working load limit. A rotten deck board under a D-ring is a securement defect, not a maintenance item for later.
Where the one-half comes from
The half-the-weight rule looks arbitrary until you read 393.102, which states the design cases the whole subpart is built on. Applied separately, tiedowns and their attachments must not exceed their working load limit under:
| Direction | Working load limit case, 393.102(a)(2) | Breaking strength case, 393.102(a)(1) |
|---|---|---|
| Forward (deceleration) | 0.435 g | 0.8 g |
| Rearward | 0.5 g | 0.5 g |
| Lateral | 0.25 g | 0.5 g |
0.8 g forward is roughly what a hard emergency stop on dry pavement puts into the load. The securement requirement then lands at one-half the article weight as the aggregate working load limit — a single, checkable number that a driver can verify at a roadside inspection without knowing anything about the deceleration cases behind it.
393.102(b) adds a requirement that gets forgotten because it is not part of the aggregate sum at all: a securement system must provide a downward force of at least 20 percent of the article weight where the article is not fully contained within the structure of the vehicle. That is the clause that makes a slack over-the-top strap a failure even when it is present and correctly routed. Tension is not optional, and it is why 393.112 requires every tiedown to be designed so the driver can tighten it in transit — steel strapping being the sole exception.
What this calculator is not
It is the general rule only. 393.106(a) is explicit that commodity-specific rules take precedence where they add requirements. Logs (393.116), dressed lumber (393.118), metal coils (393.120), paper rolls (393.122), concrete pipe (393.124), intermodal containers (393.126), automobiles and light trucks (393.128), heavy vehicles and equipment (393.130), flattened or crushed vehicles (393.132), roll-on roll-off containers (393.134) and large boulders (393.136) each have their own section. If you are hauling one of those, the general arithmetic here is a floor, not an answer.
Heavy equipment is the big one. Machinery or equipment over 10,000 lb has a separate requirement in 393.130 for tiedowns at four distinct points, in addition to the general aggregate rule. Hitting the aggregate number with three chains does not satisfy it.
Friction mats get no credit here. 393.108(g) rates an unmarked friction mat at 50 percent of the weight placed on it — but that is resistance to horizontal movement, not a working load limit, and it is not one of the three things 393.106(d) tells you to sum. Mats are genuinely useful and they are not aggregate WLL.
It does not inspect anything. Cut webbing, a cracked hook, a chain with a stretched link, a binder with a bent handle, edge protection that has cut through: 393.104(b) prohibits damaged components and none of that is visible to a calculator.
Subpart I is about commercial motor vehicles. The rules in 393.100 through 393.136 apply to trucks, truck tractors, semitrailers, full trailers and pole trailers. The arithmetic is exactly as sound behind a pickup with a landscape trailer, and using it there is a good idea, but the regulation is not by itself what makes it a legal requirement in that case.
Frequently asked questions
How many tiedowns do I need?
Run both rules and take the larger answer. 393.110 sets a minimum count from the length of the article: one tiedown if it is 5 ft or less and 1,100 lb or less, two if it is 5 ft or less but heavier, two if it is over 5 ft up to 10 ft, and over 10 ft it is two plus one more for every 10 ft or fraction beyond the first 10. Separately, 393.106(d) requires the aggregate working load limit of the tiedowns to be at least half the weight of the article. Whichever rule demands more tiedowns is the one that governs.
Does a strap over the top count double?
Only if it anchors on both sides of the vehicle. 393.106(d)(3) gives the full working load limit to a tiedown that runs from an anchor point on the vehicle, through, over or around the cargo, and then attaches to another anchor point on the other side. A tiedown that goes over the load and comes back down to an anchor on the same side falls under 393.106(d)(2) and counts as one-half, the same as a tiedown hooked directly to an attachment point on the cargo.
What is the aggregate working load limit?
The sum of the working load limit contributions of all the tiedowns securing an article, counted as one-half for a direct tiedown and for a same-side tiedown, and in full for a tiedown anchored on both sides. Under 393.106(d) that total must be at least one-half the weight of the article or group of articles being secured.
Where do I find the working load limit of my strap or chain?
On the hardware. A manufacturer marking governs under 393.108(b). If it is not marked, the tables in 393.108 supply a default, and the defaults are low on purpose: unmarked welded steel chain is treated as Grade 30 proof coil, unmarked synthetic cordage as polypropylene, and unmarked wire rope as 6 × 37 fiber core. Remember also that under 393.108(a) the working load limit of the assembly is the lowest rating of any component in it, including the ratchet or binder and the anchor point.
Does the calculator include my ratchet and my D-rings?
Only if you tell it. There is a weakest-component box for exactly that reason. 393.108(a) makes the working load limit of a tiedown the lowest rating of any of its components or of the anchor points it attaches to, and on a real trailer that is very often the stake pocket or the ratchet rather than the webbing.
What counts as blocked or braced against forward movement?
393.110(c) names a headerboard, a bulkhead, other articles which are adequately secured, or an appropriate blocking or immobilisation method. That is what allows the drop to one tiedown per 10 ft of length. A chock behind the article does not block it forward, and a tight strap is not blocking — blocking is something physical that the article would have to go through to move forward.
Why does 5/16 inch Grade 80 chain show a lower working load limit than Grade 70?
Because that is what the table in 393.108 says: 4,500 lb for Grade 80 alloy against 4,700 lb for Grade 70 transport at that one size. It is an oddity of the tabulated figures and this calculator reproduces the regulation rather than a tidied-up version of it. Marked hardware governs anyway, so a Grade 80 chain marked with its own working load limit uses that number instead.
Do friction mats count toward the requirement?
Not toward the aggregate working load limit. 393.108(g) rates an unmarked friction mat at 50 percent of the weight placed on it, but that is resistance to horizontal movement rather than a working load limit, and 393.106(d) sums only the three tiedown cases. Mats reduce the chance of the load walking and are worth using; they do not reduce the number of tiedowns the regulation requires.
Do these rules apply to my pickup and trailer?
49 CFR 393.100 scopes Subpart I to trucks, truck tractors, semitrailers, full trailers and pole trailers — commercial motor vehicles. The physics does not change behind a personal vehicle and using the same arithmetic is sound practice, but the federal rule is not by itself what makes it a legal requirement there. State law may impose its own requirements in either case.
I am hauling a skid steer. Is this enough?
No. Heavy vehicles, equipment and machinery over 10,000 lb are covered by 393.130, which requires the item to be secured at four distinct points in addition to the general aggregate working load limit rule, with accessory equipment such as a bucket or a boom secured separately. Meeting the aggregate number with fewer tiedowns does not satisfy it.