Field calculator
Crane sling load calculator (leg tension by angle)
The danger in rigging is that a sling at an angle carries far more than the load it lifts. Each leg's tension equals the load weight divided by the number of legs, divided by the sine of the sling angle measured from horizontal. Enter the load, the leg count, and the angle to get the tension per leg and the load factor. The angle drives everything: at 90 degrees (a straight vertical pull) each leg carries only its share, but as the legs spread and the angle drops, the tension multiplies. The load factor is 1.41 at 60 degrees, 2.0 at 30 degrees, and it climbs toward infinity as the angle approaches horizontal, which is why slings are rated down to a minimum angle and most riggers refuse to work below 30 degrees. Two more cautions: a four-leg bridle on a rigid load often rides on just two legs, so do not assume even sharing, and the choke or basket hitch changes the capacity. Treat this as a planning number, rig to the sling and hardware rated capacity for the actual angle, and use a qualified rigger.
Result
Sling leg tension: each leg carries (load weight / number of legs) divided by the sine of the sling angle measured from horizontal. Enter the load, the leg count, and the angle. The angle is the catch: at 90 degrees (straight vertical) each leg carries its share, but as the angle drops the tension multiplies (the load factor is 1.41 at 45 degrees and 2.0 at 30 degrees), which is why slings are rated down to a minimum angle and most riggers never go below 30 degrees. Also remember a four-leg rigid load often rides on only two legs, so do not assume even sharing. Always rig to the sling and hardware rated capacity for the angle, and use a qualified rigger.
anvilfield.com/calculators/crane-sling-leg-load-calculator · Free field calculators and FieldOS. A planning estimate, verify against the code, the manufacturer, and the engineer of record.
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Sling load FAQ
What is a qualified rigger?
A qualified rigger is a person the employer has designated who can select, inspect, and hook up rigging safely through training or experience. OSHA does not issue a rigger card; the employer determines and documents it, and ASME B30 describes the role. OSHA requires one when workers are in the fall zone during hooking or assembly.
How far must a crane stay from power lines?
Stay outside OSHA's Table A clearance: 10 ft up to 50 kV, growing with voltage to 20 ft over 200 up to 350 kV and more above that. When the voltage is unknown, default to 20 ft for lines up to 350 kV. The strongest control is to de-energize and visibly ground the line.
What is a load chart?
A load chart is the crane manufacturer's table of how much that specific machine can lift at a given radius and boom setup. Capacity drops as the load moves out to a larger radius, and the chart often subtracts the hook, rigging, and jib weight. Never exceed it. Read the deductions, not just the headline.
Why does sling angle matter?
Sling angle, measured from horizontal, sets how hard each leg pulls. The tension multiplier is 1 divided by the sine of the angle: about 1.4 at 45 degrees and 2.0 at 30 degrees, where each leg sees double. The load never got heavier, so nothing warns you. Keep the angle above 30 degrees.
How much does a choker hitch reduce sling capacity?
A choker hitch commonly de-rates a sling to around 75 to 80 percent of its vertical rated capacity, because the bend at the choke concentrates stress. A vertical hitch gives full capacity, and a basket hitch can reach twice it when the legs are vertical. Use the exact figure on the sling tag and in ASME B30.9.