Understanding Weight Limits: WLL vs MBS Explained
Why Weight Ratings Matter in Aerial Arts
When you're hanging from a piece of equipment metres above the ground, understanding the load ratings of your gear isn't just technical knowledge — it's a safety essential. Two terms you'll encounter constantly are WLL (Working Load Limit) and MBS (Minimum Breaking Strength).
What is MBS (Minimum Breaking Strength)?
Minimum Breaking Strength (MBS) is the lowest force value a product, such as a shackle or rope, is guaranteed to withstand before failure in testing. It represents the manufacturer's conservative rating to ensure safety, meaning some units might be stronger, but none should be weaker
For example, an MBS of 1 kN means the equipment will hold up 1000 kg of static force without breaking.
Important: MBS is not the weight you should load onto equipment during use. It is a laboratory figure used to calculate safe working limits.
What is WLL (Working Load Limit)?
WLL is the maximum load that should ever be applied to a piece of equipment during normal use. It is calculated by dividing the MBS by a safety factor — typically 10:1 for overhead lifting and dynamic loads like aerial arts.
WLL = MBS ÷ Safety Factor
Using the example above: 25 kN MBS ÷ 10 = 2.5 kN WLL, or approximately 250 kg.
The Safety Factor Explained
The safety factor accounts for:
- Dynamic loading (the shock load when you drop into a move)
- Material fatigue over time
- Knots and attachment methods that reduce strength
- Environmental factors (UV, moisture, heat)
- Human error in rigging
For aerial arts, a minimum 10:1 safety factor is the industry standard.
What This Means for Your Aerial Setup
If you weigh 70 kg and perform dynamic drops, your peak dynamic load could be 3–5 times your body weight during a fall arrest. That's potentially 350 kg of force. Your rigging system — from the anchor point to the swivel to the silk itself — must have a WLL that exceeds this figure at every link in the chain.
Always rate your system to the weakest component. A 500 kg WLL carabiner is only as strong as the 200 kg WLL swivel it's attached to.
Checking Your Equipment Ratings
All reputable aerial hardware will have WLL and/or MBS stamped or engraved on the equipment, or documented in the product specifications. If a piece of hardware has no rating markings, do not use it for aerial work.
At Aerial Silks New Zealand, all our rigging hardware comes with full load rating documentation. We only stock equipment rated for overhead dynamic use.
Fabric and Silk Ratings
Aerial fabrics are also rated, though the testing methodology differs from metal hardware. Our silks are tested for tensile strength. Always check that your fabric's rated load exceeds your dynamic load requirements with appropriate safety margin.
Key Takeaways
- MBS = breaking point (lab figure, not for use)
- WLL = safe working limit (use this for planning)
- Always apply a minimum 10:1 safety factor for aerial arts
- Rate your whole system to the weakest component
- Only use rated, certified hardware for overhead work
