Understanding Safe Working Load (SWL) vs. Working Load Limit (WLL): A Complete Guide for UK Businesses
Simply put -- Safe Working Load, (commonly abbreviated as SWL) is the maximum load that a piece of lifting equipment can safely handle under normal use. This is the weight limit that should never be exceeded in lifting operations. The WLL takes into consideration such factors as the design of the equipment, materials, quality of construction, and the safety factor built in by the manufacturer.
Here at Lifting Gear Direct, we get this question commonly about what the difference is between the two. And in this guide below, we’ll break down the in’s and out’s to ensure that you have a better understanding on safety and regulations– without any compromise.
So… when "SWL 500kg" is marked on a chain block for example, this means the hoist will safely lift the load up to 500 kilograms under normal working conditions. This rating is under the assumption that the equipment is in good condition, properly maintained, and used correctly in conformance with the manufacturer's specifications.
The general term used is SWL; and the lifting industry has been using this terminology for many decades. You can find it marked on older equipment, in traditional engineering specifications, and throughout operational manuals. This term is still used by many seasoned lifting equipment operators and engineers, simply out of habit and tradition.
What is Working Load Limit (WLL)?
So why do we have two different terms for the same thing? Well… WLL is the more modern term, which is increasingly preferred in current UK and European standards. You will find WLL used in newer British Standards (BS EN), contemporary equipment certifications, and modern technical documentation. This shift toward WLL is a result of international standardisation efforts to keep the consistent terminology across different countries and industries.
Despite being the newer term, WLL serves an identical purpose to SWL. Both tell you the maximum safe capacity of your lifting equipment. Whether you see SWL or WLL marked on equipment, treat them as the same thing—the load limit that must not be exceeded.
Are SWL and WLL Actually Different?
Simply put, no—Safe Working Load and Working Load Limit literally mean the same thing. They both mean the maximum weight that lifting equipment can handle safely, under normal operating conditions. Both terms literally have no underlying technical difference.
However, there are some subtle contextual differences and nuances worth noting:
Timeline of Terminology: SWL is the more traditional term, having been in use within the lifting industry since the mid-20th century. WLL appeared later, with the start of international standardisation, especially from the 1990s onward. You may notice that older equipment typically displays SWL, while newer equipment tends to show WLL.
Regional preferences are as follows: In the UK, both terms remain in common use, though WLL is increasingly dominant in official documentation. In the United States, WLL is more standard. Generally, European standards favour WLL in technical specifications.
Document Use: Modern British Standards (such as BS EN 13157 for chain blocks) use WLL. However, LOLER regulations and guidance documents from HSE sometimes use both interchangeably, recognising that numerous pieces of existing equipment carry SWL markings.
The practical takeaway? Don't worry about which term is "correct" because at the end of the day, they both mean the same thing. What matters is the practical element in never exceeding the stated capacity, regardless of whether it's labelled SWL or WLL.
Understanding Safety Factors and Breaking Strength
To understand SWL and WLL, you have to know about two related concepts -- breaking strength and safety factor. Both of these determine how the safe working load is calculated:
Breaking strength can also be referred to as ultimate strength or breaking load. This essentially is the point at which lifting equipment will fail or break… and is determined by manufacturers through thorough testing; where they load the equipment up until it fails.
The Safety Factor, also known as design factor, is the ratio of breaking strength to working load limit. This built-in margin of safety accounts for various real-world factors including wear and tear, dynamic loading, potential manufacturing variations, and unpredictable conditions.
In the industry of lifting equipment, some common safety factors are:
· Lifting slings: Typically 5:1 (breaking strength is five times the WLL)
· Chain blocks and hoists: Typically 4:1 or 5:1 depending on the type
· Shackles and fittings: Generally 6:1 for rated applications
· Wire rope: Often 5:1 for general lifting use
· Ratchet straps: Normally 3:1, but varies depending on the application
Now, let's look deeper into another realistic example. So, for instance, our LGD chain hoist with a WLL of 1000kg has been proof tested to well in excess of this capacity. Assume that it has a safety factor of 4:1; the breaking strength would, therefore, be around 4000kg. This does not mean to say that you can safely lift 4000kg because 1000kg is the WLL-the maximum safe capacity. The safety factor protects against unexpected stresses, material fatigue, and gives the all-important margin of safety.
Warning: While there is a safety factor, NEVER, under any circumstances, exceed the WLL or SWL. The margin is for protection against the unforeseen and not excess capacity that you can utilize. Overloading equipment is both illegal in the UK and dangerous, and also voids the warranty and insurances.
UK Regulations: LOLER and Marking Requirements
In the UK, the use of lifting equipment is subject to strict regulations, and understanding SWL/WLL is central to compliance.
LOLER 1998 (Lifting Operations and Lifting Equipment Regulations) requires that all lifting equipment is:
· Clearly marked with its safe working load
· Thoroughly examined at specified intervals
· Used only for loads within its capacity
· Operated by competent, trained professionals
Under LOLER, equipment should be clearly marked to indicate its SWL or WLL, in situations where this information is necessary for safe use. For example, the capacity marking should be visible and legible on items such as chain blocks, hoists, and lifting slings. Where equipment should be used in such a way that the safe working load may vary, for example, where lifting slings are used at different angles.
Further in relation to lifting equipment specifically, PUWER 1998 concluded that equipment must be appropriate to its intended use and be properly maintained. It must also only be used by people who have received adequate training. Using equipment above its WLL obviously contravenes PUWER.
The technical details of marking the equipment are provided by British Standards and European Norms.
· BS EN 13157 covers hand-operated chain hoists and specifies marking requirements
· BS EN 1492 covers textile slings. It states that different capacities need colour-coded identification.
· BS EN 818 covers short link chains and specifies how WLL should be displayed
Marking and Identification: All equipment should have its WLL or SWL permanently and legibly marked. For chain blocks, such as our Yale VSIII range, you will find the capacity stamped on the body. Lifting slings make use of colour coding for ease of identification. Shackles also have their WLL stamped onto the body.
Record Keeping: LOLER requires you to keep records of thorough examinations, including verification that equipment is being used within its rated capacity. If an incident occurs and equipment was overloaded, this creates serious legal liability.
Competent Persons: LOLER dictates that all examinations of lifting equipment are to be carried out by a "competent person"… essentially somebody with the relevant training, knowledge, and experience to identify defects and weaknesses.
How to Calculate the Required WLL for Your Application
Choosing equipment with the correct WLL isn't simply a question of matching load weight. A number of factors affect what capacity you actually need.
1. Know Your Load Weight
Start with the actual weight of what you're lifting. Yes, this sounds obvious, but it's surprising how often this gets estimated rather than measured.
Whenever possible:
· Check manufacturer specifications for the equipment you're lifting
· Use calibrated scales for all materials and components.
· Account for packaging, fixtures, and attachments
Consider moisture content for materials like timber that can absorb water
2. Add a Safety Margin
Even when you know the exact weight, it's good practice to choose equipment with capacity in excess of what is needed. A rule generally followed is that one must choose equipment rated at least 20-25% above the heaviest load one expects. This acts as a buffer for slight variations in the weight of the load, extra weight from attachments such as hooks or spreader bars, and even unexpected dynamic forces during lifting.
3. Consider Lifting Angles: Critical for Slings
This is where many people make dangerous mistakes. When lifting slings are used, the angle at which they are rigged greatly affects how much load each leg has on it.
A simple example: If using a two-leg sling for a 1000kg load:
· At 90° - (vertical lift), each leg bears 500kg
· At 60°, each leg bears approximately 577kg
· At 45° angle, each leg bears approximately 707kg
· At 30° angle, each leg bears approximately 1000kg
The shallower the angle, the higher the tension in each sling leg. That is why you should never use sling angles below 30° from vertical - the forces become dangerous. For safe operations, try to keep sling angles at 60° or steeper.
4. Consider Dynamic Loading
Static weight is one thing, but the nature of lifting operations involves movement. Dynamic forces come into play in lifting when acceleration and deceleration are involved - starting a lift, stopping a lift, moving loads horizontally whilst suspended, and sudden jerks or jolts during handling. Generally speaking, dynamic forces can increase the effective load by 25-50% or more depending on how smoothly the lift is performed.
5. Multiple Attachment Points
With systems like our mobile gantry or when lifting with multiple slings, some consideration has to be given to how the weight of a load is distributed. You cannot assume that the weight will divide out evenly; the centre of gravity is everything. If a load is perfectly balanced and you are using four lifting points, then each point bears roughly 25% of the total weight. However, if the centre of gravity is off-centre, one or two points might bear considerably more. Unless you have calculated the exact centre of gravity, it is best to assume the weight distribution will be uneven.
Practical Example
Suppose that you have to lift a piece of machinery weighing 1500kg using a two-leg lifting sling at an angle of about 60°.
· Load weight: 1500kg
· With 60° angle, each leg bears approximately: 1500kg ÷ 1.732 = 866kg per leg
· Add safety margin (25%): 866kg × 1.25 = 1,083kg per leg
· Account for dynamic loading: round up to be safe
Result: You'd want to pick a lifting sling where each leg has a WLL of at least 1,200kg, which would commonly be a 2 tonne sling - 2000kg WLL per leg when used in choke or basket.
Common Mistakes That Compromise Safety
Knowing SWL and WLL is one thing and applying that knowledge correctly is another. Here are errors to avoid:
Confusing Breaking Strength with WLL
Some individuals see a certain piece of equipment has a breaking strength of 5000kg and believe they can lift 5000kg safely. This is incorrect and is dangerous. Breaking strength is not the capacity that one can actually work to; it is actually the failure point. Always work within the WLL or SWL, as that safety factor has been calculated.
Ignoring Sling Angle Effects
As noted above, shallow angles increase the load on each leg substantially. We have seen cases where a 1000kg per leg rated sling was used at a 30° angle to lift a 1000kg load. In fact, each leg was subjected to nearly 1000kg of tension—right on the limit. Even the slightest mistake and added movement would cause a failure.
Failure to Account for Worn or Damaged Equipment
The WLL marked on equipment assumes it is in good condition and under damaged. Wear and tear, corrosion, cuts, abrasions, or any damage reduces the actual safe capacity. A lifting sling with cuts or abrasion might only have 50% of its original strength, even though it still shows the original WLL marking. This is why regular inspections under LOLER are mandatory.
Overlooking Dynamic Forces
Static load predictions/calculations may be fine for planning purposes, and when it comes to actually conducting a lift, there is always the element of lift cycle motion. Shock loading—jolting or dropping a load suddenly—can develop forces several times greater than the static weight. Operations need to be smooth and controlled.
Failure to Inspect Before Use
LOLER requires written schemes of in-service thorough examinations to be carried out every so often, (normally 6-12 months), operators must also carry out pre-use visual checks. Look for: Legible capacity markings Signs of wear or damage Bent or stretched components Corrosion or chemical damage Missing or damaged safety catches on hooks Questionable equipment should not be used. The WLL that has been assigned to damaged equipment no longer stands.
WLL and SWL Across Different Equipment Types
Different types of lifting equipment display and use WLL/SWL in slightly different ways. Here's what you need to know for common equipment categories:
Manual Chain Blocks and Hoists
Chain blocks such as our Yale 360 range and the LGD chain hoist have their SWL or WLL stamped clearly into the body, usually within the metal housing. Capacities can start at 250kg for compact units such as the Kito CX mini chain block and go right up to 20,000kg for heavy-duty industrial hoists. The stated capacity applies when the hoist is used vertically for straight lifting.
Electric Hoists
Electric chain hoists and wire rope hoists operate on the same principles. Our range of Delta electric hoists and Yale CPV/F clearly states its rated capacity. Electric hoists have other factors to consider, and most models have a different WLL for continuous and intermittent usage. More importantly, running continuously at full capacity generates more heat and wear.
Lifting Slings
In reality, lifting slings are more complex because their effective WLL depends on how they are used:
· Straight lift (single leg): WLL marked on sling applies
· Choke hitch: Normally reduces WLL to 80% of the marked capacity
· Basket hitch (two legs vertical): Effectively doubles the WLL
· Basket hitch at angles: Multiply capacity by angle factor to obtain actual capacity per leg
Colour coding for rapid identification is used by round slings and flat webbing slings:
· Purple = 1 tonne
· Green = 2 tonnes
· Yellow = 3 tonnes
· Grey = 4 tonnes
· Red = 5 tonnes
· Brown = 6 tonnes
· Blue = 8 tonnes
· Orange = 10 tonnes
Colour represents the WLL in a straight vertical lift. Always check the label for specific information, including the manufacturer, batch number and certification.
Shackles & Lifting Points
Shackles such as our bow shackles and dee shackles have their WLL marked permanently on the body. The rating applies when the shackle is properly loaded—commonly along the centreline of the bow or dee. Side-loading a shackle may reduce its safe capacity by 50% or more.
Wire Rope and Chain Slings
Both wire rope slings and chain slings work similarly to textile slings where their WLL are based upon the configuration that they are used in. Wire rope tends to have higher capacities for equivalent thickness, but requires more careful inspection for broken wires and wear.
Mobile Gantry Systems
The WLL is clearly displayed on our bespoke mobile gantry range available from 500kg to 5000kg capacity. The stated capacity refers to the whole gantry system when it is properly assembled, levelled and brakes or parking jacks are applied. The gantry should never be moved when loaded.
Ratchet Straps and Lashing Equipment
Ratchet straps and cam buckle straps usually have both a WLL and a breaking strength marked on them. A ratchet strap might be marked "LC 2000kg / BS 4000kg" meaning a lashing capacity (WLL) of 2000kg and breaking strength of 4000kg. Use the WLL figure and remember that the strap should restrain cargo, not lift it vertically.
Choosing the Right Equipment from Lifting Gear Direct
Understanding WLL and SWL is your starting point for selecting the right gear for your needs.
For Manual Lifting:
· Compact jobs up to 500kg: Kito CX mini chain block
· General workshop use 500kg - 5000kg: LGD chain hoist, Delta CY chain block, Yale VSIII
· Heavy-duty industrial work up to 20,000kg: Yale 360 chain block, Raptor MH chain block
· Awkward positions and precise control: Lever hoists of the type Tractel Tifor
For Powered Lifting:
· Light-duty electric hoists: Delta DEH range - fast UK delivery, often next day
· Industrial applications: Yale CPV/F with integrated trolley
· High-speed operations: Variable speed controlled models available.
· Explosive atmospheres: ATEX-rated electric hoists for hazardous environments
For Load Attachment:
· General purpose: Round slings and flat webbing slings (color-coded by capacity)
· Heavy loads or harsh environments: Chain slings and wire rope slings
· Secure connections: wide range of shackles, hooks, and connectors
· Specialised loads: Lifting clamps, drum handlers, and magnetic lifters
For Crane Systems:
· Fixed positions: Wall-mounted, column-mounted, or floor-mounted jib cranes
· Flexible workspace: Mobile gantry systems (bespoke manufactured in our West Midlands workshop)
· Portable jobs: Aluminium gantry systems (lightweight, foldable)
· Small workshops: Engine cranes and floor cranes
For Height Safety:
· Working at height: Full body harnesses, safety lanyards, fall arrest blocks
· Anchor points may be roof anchors, beam anchors, or tripod systems.
· Specialised environments: ATEX-rated height safety equipment
The WLL or SWL is visibly indicated on every product page of our website, along with full details for specifications to enable you to make your choice. If you are not sure what capacity you require, then our experienced team is able to advise based on your application.
Inspection and Maintenance to Preserve Safe Capacity
The WLL marked on your equipment only remains valid if the equipment is properly maintained and in good working condition. Regular inspection and maintenance are a legal requirement under LOLER; they are essential to and for overall safety.
Pre-use visual checks should be carried out before every use:
· Check that capacity markings are visible and legible
· Look for obvious damage, wear or deformation
· Verify all safety features are functional: brake, safety latches, etc.
· Make sure moving parts operate smoothly.
· Check for corrosion or chemical damage
The thorough examinations under LOLER must be carried out by a competent person:
· Lifting equipment for people: every 6 months
· Other lifting equipment: Every 12 months (or more frequently if recommended by manufacturer)
· Accessories such as slings and shackles: Every 6 months in normal usage
When Equipment Should Be Retired:
· Any deformation of the load-carrying parts
· Cracks or fractures visible
· Excessive wear (usually 10% reduction in diameter for chains and wire rope)
· Damage to textile slings: cuts, chemical damage, heat damage, UV deterioration
· Identification markings missing or illegible
· Any doubt about safety
Don't take chances with questionable equipment. The cost of replacement is small compared to the consequences of equipment failure – which can be catastrophic.
Proper Storage Extends Life:
Keep equipment clean and dry Store slings flat or hung up (not knotted or coiled tightly) Protect from UV light, chemicals, and extreme temperatures. Keep manual chain blocks lubricated according to manufacturer guidance Store in designated areas away from traffic and potential damage
Getting Expert Advice from us here at Lifting Gear Direct
Selecting the right lifting equipment with appropriate WLL ratings is not always straightforward. There is consideration for load calculations, angle factors, and dynamic forces, among other specific application requirements. This is where our experience helps.
Serving UK businesses for nearly 20 years across construction, manufacturing, engineering, automotive, and countless other sectors, we have seen virtually every lifting scenario. Our team includes qualified engineers who can:
· Calculate the correct WLL requirements for your particular application
· Recommend appropriate types of equipment for your loads and environment
· Design and fabricate custom solutions, such as custom-sized mobile gantries and jib cranes.
· Provide LOLER inspection and certification services
· Offer on-site testing and installation.
· Deliver emergency breakdown support
Final Thoughts: Safety Always Comes First
The expressions Safe Working Load and Working Load Limit are identical in meaning, referring to the maximum capacity of the lifting equipment under normal use. Whether it is SWL or WLL on your equipment, treat it as the limit that must never be exceeded.
The regulations exist for good reasons. Equipment failure during a lifting operation can lead to fatal injury and serious property damage, sometimes with devastating consequences for business. Understanding and respecting WLL ratings is a key foundation to safe operation.
Some of the most notable points to remember include:
· SWL and WLL are the same thing, only different words and terminology.
· Do not exceed the maximum stated value, even though safety factors are built in
· When doing your calculations, consider the angles of the slings, the dynamic forces and the load distribution. Different equipment types have different considerations for their WLL.
· Regular inspection and maintenance is both required by law and is necessary.
· When in doubt, do not guess - seek expert guidance.
For us here at Lifting Gear Direct, safety is not only a value to us, but it is at the centre of everything we do.
From the equipment we stock and the guidance we give, we are dedicated to supporting UK businesses function safely and within the law.
Visit our site to see all the lifting equipment we offer, or if you need more information and guidance on selecting the appropriate capacity equipment to meet your needs, call our team at 01384 76961 or reach us via our contact page.
