How to use the wire rope weight and SWL calculator
Before a lift you need two numbers about the rope itself: how much it weighs and how much it may carry. This calculator derives weight per foot and total weight from the nominal diameter and core type, then divides the minimum breaking strength by the design factor to give the safe working load. For long vertical runs it also subtracts the rope weight so you can see the capacity actually left for the load.
Weight per foot uses the standard approximate factors of 1.50 lb/ft per square inch of diameter for fiber core and 1.60 for IWRC. Breaking strength should come from the manufacturer catalog or the certificate supplied with the rope. Leave that field blank and a deliberately conservative estimate based on diameter and grade is used instead, which is fine for planning but never for final rigging decisions.
OSHA 1926.251 and ASME B30.9 set a minimum design factor of 5 to 1 for wire rope slings in general rigging. Remember that an angled sling leg carries more tension than a vertical pull, so this safe working load is not the same as the weight the rigging can lift once the legs are spread.
Confirm the crane load chart and the rating of every component in the rigging - rope, shackles, hooks and hardware - and have a qualified rigger inspect the assembly before the lift. Any rope past the removal criteria for broken wires, diameter loss or corrosion must be taken out of service.
Frequently asked questions
OSHA 1926.251 and ASME B30.9 require a minimum design factor of 5 to 1 for wire rope slings used in general rigging. Personnel lifting and other critical lifts use higher factors set by the applicable standard.
No. The estimate here is a deliberately conservative figure derived from diameter and grade, and it will differ from a real product. Always enter the minimum breaking force from the manufacturer catalog or the certificate that came with the rope.
Remove a rope with broken wires beyond the allowable count in one lay, with diameter reduction past the limit in the applicable standard, or with severe kinking, crushing, birdcaging or corrosion. A qualified person must make that determination during periodic inspection.