Whether you’re lifting with cranes, hoists, slings, shackles, or wire rope, every rigging decision depends on one number: the Working Load Limit (WLL).
If workers don’t understand WLL, breaking strength, design factors, or sling angles, it becomes easy to overload equipment, and that’s how gear fails, loads drop, and workers get hurt.
This guide explains WLL in simple terms so your crew can make safe decisions on the job.
Working Load Limit (WLL) is the maximum weight a piece of rigging equipment can safely lift under normal conditions.
You’ll also hear the terms:
Safe Working Load (SWL)
Rated Capacity
Allowable Load
All of these refer to the same thing: the safe limit, not the point where equipment breaks.
The manufacturer assigns the WLL based on testing and industry standards.
Breaking Strength (also called ultimate strength or tensile strength) is the point at which the gear actually fails during destructive testing.
Breaking strength is NOT the number you use in the field.
Why?
Because breaking strength has zero safety margin built in. If you rig to breaking strength, the gear will fail.
| Term | What It Means | Safe to Use in the Field? |
|---|---|---|
| Breaking Strength | The point where gear physically breaks | ❌ No |
| Working Load Limit (WLL) | The maximum safe load under normal use | ✅ Yes |
| Design Factor | The built-in margin between WLL and breaking strength | Informational |
Manufacturers determine WLL using this simple formula:
Common design factors:
| Equipment Type | Typical Design Factor |
|---|---|
| Chain Slings (Grade 80/100) | 4:1 |
| Wire Rope Slings | 5:1 |
| Synthetic Web Slings | 5:1 |
| Round Slings | 4:1 or 5:1 |
A higher design factor = more built-in safety.
Breaking Strength: 20,000 lbs
Design Factor: 5
WLL = 20,000 ÷ 5 = 4,000 lbs
Breaking Strength: 10,000 lbs
Design Factor: 5
WLL = 2,000 lbs
Breaking Strength: 40,000 lbs
Design Factor: 4
WLL = 10,000 lbs
These simple calculations help workers understand how gear capacity is determined.
Even when the sling is rated correctly, angles can instantly reduce its capacity.
The wider the angle, the more tension is placed on each sling leg.
Example:
| Sling Angle | Load on Each Leg |
|---|---|
| 60° | 115% of load |
| 45° | 141% of load |
| 30° | 200% of load |
So a 1,000 lb load at 30° can put 2,000 lbs of force on each sling leg.
This is why workers need to understand angles; it’s one of the leading causes of overloaded rigging gear.
Even if equipment is tagged properly, the actual WLL can be reduced by:
cuts, tears, abrasion
knots in slings
chemical exposure
extreme temperatures
UV breakdown on synthetic slings
side loading shackles
wrong hitch type (choker, basket, vertical)
damaged or missing tags
If the tag is missing, frayed, unreadable, or questionable → remove it from service.
These standards define how WLL is determined and used:
OSHA 1910.184 – Slings
ASME B30.9 – Slings
ASME B30.10 – Hooks
ASME B30.26 – Rigging Hardware
Key rules:
Employers must ensure rigging is used within WLL
Tags must be readable
Workers must be trained to calculate loads
Damaged gear must be removed from service
Inspections must be performed regularly
Training isn’t optional, it’s part of compliance.
Most rigging incidents come down to lack of training, not bad equipment.
Safety Evolution offers:
✔ Crane & Rigging Certification
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No. Exceeding WLL can cause immediate equipment failure.
No. Breaking strength is the maximum force before failure.
WLL is the safe working limit.
Yes, these terms are often used interchangeably.
Before each use
Periodically (per manufacturer/OSHA)
After shock loading
Any time damage is suspected
Remove it from service immediately.
Yes, OSHA requires workers to be competent and trained.
Understanding Working Load Limit (WLL), breaking strength, design factors, sling angles, and inspection requirements is essential for safe lifting.
If your team rigs loads, operates cranes, or works around lifting equipment, training isn’t optional — it’s what keeps people safe and keeps jobs moving.
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