Sling Angle Calculator

The tension factor is 1/sin(angle), where the angle is measured from horizontal. At 90° (vertical) the factor is 1.0; at 60° it is 1.155; at 45° it is 1.414; at 30° it is 2.0. Multiplying the vertical load share per leg by this factor gives the actual tension in the leg.

Only the vertical component of sling tension (T × sin θ) supports the load; the horizontal component squeezes the load. As the angle drops, total tension must grow to hold the same weight. At 30°, each leg carries twice its vertical share.

ASME B30.9 recommends sling angles never fall below 30° from horizontal. Below that, tension exceeds twice the vertical share. If hook height forces a shallow angle, use a spreader beam to bring legs back toward vertical.

Only when legs are the same length, attach at the same height, and the load's center of gravity is centered. Unequal lengths or an off-center CG require a qualified person to evaluate the rig per ASME B30.9.

A spreader beam keeps sling legs parallel (near vertical) by pushing the attachment points apart. Use one when: the load is too wide to rig directly, the lifting points cannot handle horizontal squeeze, or the natural sling angle would fall below 45°. A balanced spreader beam eliminates horizontal compression entirely.

When sling legs angle inward, they produce a horizontal compressive force on the load's lift points. Formula: H = (load ÷ legs) ÷ tan(angle). At 45° with a 2-leg, 10-tonne lift, each leg imposes 5 t of inward squeeze. Verify lift points and packaging can withstand this load.

At exactly 90° (perfectly vertical), the tension factor is 1.0 and each leg operates at its full rated WLL. At 60°, effective capacity drops to 86.6%; at 45° to 70.7%; at 30° to only 50%. This is why rigging at higher angles is always preferred.

Chain slings are most durable, heat-resistant, and adjustable — use for abrasive or sharp-edged loads, high temperatures, or where length adjustment is needed. Wire rope slings offer high strength with some flexibility — general rigging, outdoor use. Web (flat) slings are lightweight and won't mar soft or painted surfaces — use for finished goods and delicate loads.