WLL means working load limit. It is the maximum load a piece of lifting equipment, such as a sling, shackle, hook or chain, is rated to carry in normal service, under the conditions the manufacturer states. The WLL is marked on the equipment. You never load it beyond that figure, and you never use gear that has lost its marking.
WLL is not the same as the breaking load. The manufacturer sets the WLL well below the load that would break the item, using a design factor. The formula is WLL = minimum breaking load ÷ design factor. For example, a sling with a minimum breaking load of 10,000 lb and a design factor of 5 has a WLL of 2,000 lb.
WLL meaning and related terms
| Term | Meaning | Notes |
|---|---|---|
| WLL (working load limit) | The maximum load the item is rated to lift in general service, as marked by the manufacturer. | The term OSHA uses alongside rated capacity. OSHA 1926.251 describes rated capacities “i.e., working load limits”. |
| SWL (safe working load) | The older term for the same idea. | Still used in some company rules and in UK law. LOLER regulation 7 requires lifting machinery and accessories to be marked with their safe working loads. For a crane, the figure comes from its load chart. |
| MBL or minimum breaking load | The least load at which the item is expected to fail in testing. | Never a working figure. It is the starting point for the WLL. |
| Design factor | The ratio between the minimum breaking load and the WLL, also called safety factor. | A design factor of 5 is written 5:1 and means the WLL is one fifth of the minimum breaking load. |
| Rated capacity | A manufacturer’s rating for a machine or an accessory, often for a stated configuration. | For slings and hardware it is the same idea as WLL. For a crane it depends on boom, radius and set-up. |
| Proof load | A test load applied above the WLL, for example on custom lifting accessories. | OSHA 1926.251(a)(4) requires custom grabs, hooks and clamps to be proof-tested to 125 percent of their rated load before use. |
How WLL is calculated
Manufacturers test samples to find the minimum breaking load, then divide by a design factor set by the product standard. You use the result, not the formula, in practice. If a piece of gear has no WLL marking, do not work one out yourself and use it. OSHA 1926.251(a)(2) requires rigging equipment to have legible identification markings that show the recommended safe working load, and says it must not be used without them.
| Equipment | Typical design factor | Example: MBL to WLL |
|---|---|---|
| Alloy steel chain | 4:1 | MBL 8,000 kg gives a WLL of 2,000 kg |
| Wire rope sling | 5:1 | MBL 10,000 kg gives a WLL of 2,000 kg |
| Synthetic web or round sling | 5:1 in US practice, 7:1 in European practice | MBL 14,000 kg gives a WLL of 2,000 kg at 7:1 and 2,800 kg at 5:1 |
These are typical figures quoted by sling suppliers, and sources differ on synthetic slings: US guidance based on ASME B30.9 quotes 5:1, and European sources quote 7:1. The numbers in the examples are illustrative. Your equipment’s marked WLL always overrides a table.
Sling angle changes the WLL
A sling’s WLL is stated for a particular hitch and angle. When two legs lift a load and the angle between each leg and the horizontal gets smaller, the tension in each leg rises, so the usable capacity of the pair falls. For a two-leg sling the capacity of the pair is twice the single-leg vertical WLL times the sine of the angle from the horizontal.
| Angle of each leg from the horizontal | Capacity of a two-leg sling, as a share of 2 × single-leg WLL | Example with a 2,000 kg single-leg vertical WLL |
|---|---|---|
| 90 degrees (vertical legs) | 100 percent | 4,000 kg |
| 60 degrees | 87 percent | 3,464 kg |
| 45 degrees | 71 percent | 2,828 kg |
| 30 degrees | 50 percent | 2,000 kg |
Many sling tags show WLL at set angles, and sling charts do the same job. Use the tag, or see the sling graph guide. At 30 degrees each leg carries a force equal to the full weight of the load, which is why small angles are avoided. Never go below the lowest angle on the tag.
Where to find the WLL
| Equipment | What OSHA 1926.251 requires on the marking |
|---|---|
| Alloy steel chain sling | Size, grade, rated capacity and the sling manufacturer, permanently affixed and durable ((b)(1)). |
| Wire rope sling | Size, rated capacity for the hitch types used and the angle it is based on, and the number of legs if more than one ((c)(16)). |
| Fiber rope sling | Rated capacity for the hitch types and angle, the fiber material and the number of legs ((d)(7)). |
| Synthetic web sling | Manufacturer’s name or trademark, rated capacities for the hitch types and the type of material ((e)(1)). |
| Shackles | Rated capacity marked on the shackle, and not exceeded ((f)(1)). |
| Hooks | Follow the manufacturer’s recommendations. Hooks without them must be tested to twice the intended safe working load before first use, and the test recorded ((f)(2)). |
What reduces or ends the usable WLL
- Damage or wear. Defective rigging equipment must be removed from service, and it must be inspected before each shift and as needed during use (1926.251(a)(1)).
- Shock loading. Shock loading of slings is prohibited (1926.251(c)(11)). A sudden jerk can put much more force on the gear than the load’s weight.
- Heat. Natural and synthetic fiber rope slings may be used from minus 20 to 180 degrees Fahrenheit without lowering the WLL, and the manufacturer’s advice applies outside that range (1926.251(d)(3)). Polyester and nylon web slings must not be used above 180 degrees Fahrenheit (1926.251(e)(7)).
- Chemicals. Nylon web slings must not be used where acid or phenolic fumes or liquids are present, and polyester and polypropylene web slings must not be used where caustics are present (1926.251(e)(6)).
- The weakest part. The component with the lowest WLL sets the limit for the whole assembly. A 10-tonne hook, a 6-tonne master link and a 4-tonne chain leg make a 4-tonne assembly. OSHA also requires hooks, rings and links used with alloy steel chain to have a rated capacity at least equal to the chain (1926.251(b)(2)).
- Wrong weight. You must know the load weight, from the manufacturer, a recognized calculation or an equally reliable source (1926.1417(o)(3)).
Safe use checklist
- Find the load’s weight, including slings, shackles and spreader beams.
- Read the WLL on every item in the lifting chain for the hitch and angle you will use.
- Check that the lowest WLL in the chain is higher than the load.
- Inspect each item before use and remove anything damaged or unmarked.
- Use padding or protection on sharp edges.
- Lift smoothly with no jerks and keep people clear of the load path.
- If anything is unclear, stop and ask a competent person.
Questions about WLL
What does WLL stand for?
Working load limit. In older documents and in UK law you will also see safe working load, or SWL.
Is WLL the same as SWL?
They describe the same idea for most lifting accessories. WLL is the term used in modern product standards and by OSHA alongside rated capacity. SWL is the older term and is still used in LOLER and some company rules. For a crane, the limit comes from the load chart for the current set-up.
Can I load gear a little over its WLL?
No. The margin between the WLL and the breaking load exists to cover things like shock, wear and hitch effects. It is not spare capacity. OSHA says rigging must not be loaded beyond its marked safe working load (1926.251(a)(2)).
Does WLL change with the angle?
Yes, for multi-leg slings and for choker and basket hitches. The sling tag or chart gives the WLL for each configuration.
What if the tag is missing or unreadable?
Take it out of service. OSHA says rigging must not be used without legible markings (1926.251(a)(2)(iii)). Ask the manufacturer or a competent person whether it can be re-identified.
Related reading: three types of slings, lifting and rigging procedures, the mobile crane lifting plan and rigging hand signals.
Sources (checked 31 October 2026)
- OSHA 29 CFR 1926.251, Rigging equipment for material handling
- OSHA 29 CFR 1926.1417, Operation
- UK Lifting Operations and Lifting Equipment Regulations 1998, regulation 7, Marking of lifting equipment
- Mennens, The difference between WLL, SWL and MBL (supplier guide, European practice: design factors 4:1 chain, 5:1 wire rope, 7:1 synthetic slings).
- Safety Evolution, Working Load Limit (WLL) guide (supplier guide, US practice: 10,000 lb breaking strength at 5:1 gives 2,000 lb WLL). ASME B30.9 is the US sling standard it refers to; its synthetic web sling design factor is quoted by suppliers as a minimum of 5:1. The two guides differ on synthetic slings, which is why the table shows both.
General information only. Follow the manufacturer’s marking and instructions, and the rules in your jurisdiction.