Working Load Limit (WLL) vs Safe Working Load (SWL) – Definitions, Differences and Calculations

What Is WLL (Working Load Limit)?

When selecting lifting equipment for industrial operations, understanding load capacity terminology is critical for safety and regulatory compliance. Two terms you'll frequently encounter are Working Load Limit (WLL) and Safe Working Load (SWL). While these terms are often used interchangeably, modern safety standards have made important distinctions that every lifting equipment operator needs to understand.

This comprehensive guide explains what WLL and SWL mean in modern regulations, how these values are calculated, and the key differences between WLL, SWL, and Maximum Rated Capacity (MRC).

What Is SWL (Safe Working Load)?

The terms working load limit (WLL) and safe working load (SWL) both refer to the maximum weight that a given piece of equipment can safely lift. For example, if a chain hoist has a WLL or SWL of 500kg, it should not be used to lift loads that weigh more than 500kg.

The terms WLL and SWL are often used interchangeably. The Lifting Operations and Lifting Equipment Regulations 1998—better known as LOLER—favour the term ‘safe working load’, stating that…

“All lifting equipment, including accessories, must be clearly marked to indicate their 'safe working loads' (SWL) - the maximum load the equipment can safely lift.”

However, in more recent years, WLL has replaced SWL as the preferred term in most formal usage. For instance, ISO 17096:2015 (an international standard that focuses on load lifting attachments for cranes) uses the term ‘working load limit’, defining this as “the maximum load the attachment is designed to lift under the conditions specified by the manufacturer”.

In most cases, it doesn’t really matter whether you use the term WLL or SWL—both are widely understood to mean ‘the maximum load this product was designed to lift’.

That said, some people do use the two terms to differentiate between the product’s maximum lifting capacity in ideal conditions and the maximum load that can be safely lifted in the present circumstances.

WLL vs SWL

When the terms WLL and SWL are used to refer to two different figures, this is usually what is meant:

• Working Load Limit (WLL) is the maximum load that a piece of lifting equipment is designed to safely lift under optimal conditions as specified by the manufacturer. This is the standard term used in modern safety regulations and international standards. The term "Working Load Limit" is the preferred terminology in contemporary safety standards. ISO 17096:2015, an international standard focusing on load lifting attachments for cranes, defines WLL as: "The maximum load the attachment is designed to lift under the conditions specified by the manufacturer." This definition emphasizes that WLL is determined by manufacturers based on rigorous testing and engineering calculations, incorporating appropriate safety factors to ensure safe operation.
  
  
• Safe Working Load (SWL) traditionally referred to the maximum weight a piece of lifting equipment could safely handle. Historically, SWL was the standard term used across the industry and appears in older regulations, including the Lifting Operations and Lifting Equipment Regulations 1998 (LOLER). However, the term "safe" created legal ambiguity. It implied that as long as operators stayed within the SWL, the operation would be completely safe regardless of other factors, which is not always the case. Variables such as sling angles, dynamic loading, and environmental factors all affect the actual safe capacity.

How WLL Is Calculated

WLL = Minimum Breaking Strength (MBS) ÷ Safety Factor (SF) Where:

• Minimum Breaking Strength (MBS) = The minimum force at which the equipment will fail structurally
• Safety Factor (SF) = A multiplier that provides a margin of safety

How WLL Is Calculated

UK Regulatory Note: While international ISO/EN standards have moved to WLL terminology, LOLER 1998 still references SWL. Both terms are legally acceptable in the UK and mean the same thing. Equipment marked with either SWL or WLL is compliant.

Frequently Asked Questions

What is working load limit?

Working Load Limit (WLL) is the maximum load that lifting equipment is designed to safely lift under the specific conditions outlined by the manufacturer. It is calculated by dividing the equipment's minimum breaking strength by an appropriate safety factor.

What's the difference between SWL and WLL in UK regulations?

In UK practice, both terms mean the same thing—the maximum load equipment is designed to lift. LOLER 1998 uses 'SWL' terminology, while modern ISO and EN standards prefer 'WLL' for consistency. Both terms remain legally valid in the UK. You'll see SWL on older equipment and LOLER certificates, while newer products typically display WLL to align with international standards.

How are working load limits calculated?

WLL = Minimum Breaking Strength (MBS) ÷ Safety Factor (SF). The manufacturer determines the breaking strength through rigorous testing, then applies an appropriate safety factor (typically 4:1 to 7:1).

What is the difference between WLL and rated capacity?

WLL refers to the maximum capacity of individual lifting accessories (below the hook). Rated Capacity (MRC) refers to the maximum load a complete lifting machine (crane/hoist) can lift in a specific configuration.

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At SafetyLiftinGear, we are committed to providing our customers with top-quality lifting gear alongside all the information required to use the equipment safely. That’s why we always display the working load limit (WLL) on our product pages.

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For more information about our products and their load capacities, please don’t hesitate to get in touch and a member of our team will be happy to help.