Safe Working Load, sling angle de-rating, and multi-leg tension — for lifting supervisors and riggers to verify a rated capacity before a lift, not to replace a certified lifting plan.
kg
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SWL / WLL = MBL ÷ Factor of Safety. Always confirm the manufacturer-certified FoS on the equipment tag — this is a general guide, not a substitute for the certificate.
SWL / WLL
—
kg
MBL—
FoS—
kg
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90°
60°
45°
30°
90°
Angle is read between the sling leg and the horizontal plane — not from vertical. A shallower angle (closer to the load) sharply increases tension in each leg.
DE-RATED SWL / WLL
—
kg
Angle factor—
Rated (90°)—
kg
tonnes
TENSION PER LEG
—
kg
Effective legs—
Angle factor—
Quick reference — before you lift
Typical factors of safety
Wire rope slings — 5:1
Chain slings — 4:1
Synthetic web / round slings — 5:1 to 7:1
Lifting appliances (cranes, hoists) — per manufacturer / standard
Common mistakes to avoid
Ignoring sling angle reduction
Guessing load weight instead of confirming it
Mixing uncertified lifting gear
Using damaged or modified equipment
Assuming all slings have equal capacity
Always include in total load
The item being lifted
Slings, shackles, and hooks
Rigging gear and any attached contents
Best practice
Never exceed the lowest-rated component in the system
Check certificates, tags, and markings before use
Use a competent lifting supervisor and trained riggers