How much does a sling angle add to the tension?

Why the angle matters so much

A sling hanging straight up carries exactly its share of the weight. Tilt the legs outward and each one must pull up on the load and also inward against the other leg, so the tension rises even though the load has not changed. The geometry is a force triangle: the vertical part of each leg's tension must equal its share of the weight, W ÷ n, so the tension is that share divided by sin θ, where θ is the angle between the leg and the horizontal. Because sin θ shrinks quickly below 45°, a sling that is comfortable at 60° can be overloaded at 25°. Sling capacities are therefore rated for a stated angle, and OSHA requires wire rope and fiber rope slings to carry a tag that gives the rated capacity for each hitch and the angle on which it is based (29 CFR 1910.184(f)(1) and (h)(1); 1926.251).

The formulas

Tension per leg T = W ÷ (n × sin θ). Load factor = 1 ÷ sin θ (the tension of one leg divided by its straight-up share). Capacity of the sling at angle θ = n × WLL × sin θ, where WLL is the rated load of one leg hanging straight up. Smallest angle θ = arcsin(W ÷ (n × WLL)). Included angle between two legs = 180° − 2θ. From geometry, sin θ = H ÷ L for a hook height H over legs of length L, and cos θ = (S ÷ 2) ÷ L for pick points S apart. These are trigonometry, not rules from a standard; the standards set the ratings and the limits on use.

Worked example

A 2,000 lb pump is lifted with a two-leg sling. At 60° from the horizontal each leg carries 1,155 lb (load factor 1.155); at 45° it carries 1,414 lb (1.414); at 30° it carries 2,000 lb, double its straight-up share. The legs of the sling are rated 2,000 lb each straight up. A 3,000 lb load needs sin θ = 3,000 ÷ (2 × 2,000) = 0.75, so the legs must make at least 48.6° with the horizontal. At 45° the sling can carry only 2,828 lb, and at 30° only 2,000 lb, so the 3,000 lb load would overload it at either. The calculator opens with this 2,000 lb lift at 60°.

Limits of this method

• Equal sharing is an idealization. The formula divides the load evenly over the n legs. With a rigid load and three or four legs, one or two legs often carry most of it, because of slightly different leg lengths or pick points. For 3 or 4 legs on a rigid load this page therefore counts only 2 legs (n = 2) in all three modes; use the sling maker's rated capacity for the sling you have. The sling maker's rating and a qualified person decide how many legs may be counted.
• It gives tension in the leg, not the rating of the whole rig. Hooks, shackles, master links, and the pick points on the load each have their own limits, and Crosby's guidance says shock loading, sharp corners, small bend radii and choker hitches reduce the working load further. A chain sling in a choker hitch, for example, must be reduced by 20% (Crosby catalog).
• Static loads only. Snatching, swinging or sudden stops add forces that the formula ignores.
• The load must hang level and the center of gravity must be known. Off-center loads put more of the weight on one leg and change the angles.
• The 30° limit is a floor, not a target. Where the tag of your sling gives a minimum angle, that figure rules.

Common questions

How do you calculate the tension in a sling leg?

Divide the load by the number of legs (this page counts at most 2 legs, even if you pick 3 or 4, because a rigid load rarely shares evenly) and by the sine of the angle the leg makes with the horizontal: T = W ÷ (n × sin θ). A 2,000 lb load on two legs is 1,000 lb per leg when the legs hang straight up, 1,155 lb at 60°, 1,414 lb at 45° and 2,000 lb at 30°, the whole weight on each leg. The factor 1 ÷ sin θ is called the load factor: 1.155 at 60°, 1.414 at 45°, 2.000 at 30° and 3.86 at 15°.

Why is a small sling angle dangerous?

Each leg must carry its share of the weight upward and also pull inward against the other leg. As the legs lie flatter, the sideways pull grows and the tension climbs without limit: at 30° each leg of a two-leg sling carries as much as the whole load, and at 15° it carries 1.93 times the load. The slings, the hooks and the pick points of the load see that tension too. Sling makers' warnings say never to rig a sling with an angle less than 30° to the horizontal (Crosby Group catalog), and ASME B30.9 is quoted as barring it unless the manufacturer or a qualified person recommends it.

Is the angle measured from the horizontal or the vertical?

Rated capacities on slings are given for an angle measured from the horizontal, which is what this calculator uses. OSHA's definition of the angle of loading (29 CFR 1910.184(b)) allows either, measured from the horizontal or the vertical plane, and treats a leg within 5° of the vertical as a vertical leg. A common mistake is to type the angle from the vertical, 30° instead of 60°, and read a tension far too low. Check which reference your tag or chart uses.

How do I find the minimum angle for my sling?

Use the rated load of one straight-up leg. For 3 or 4 legs on a rigid load this page counts only 2 legs; use the sling maker's rated capacity for the sling you have. The legs can carry the load at angle θ when n × WLL × sin θ is at least the load, so sin θ = load ÷ (n × WLL). Two legs rated 2,000 lb each under a 3,000 lb load need sin θ = 3,000 ÷ 4,000 and an angle of at least 48.6° from the horizontal. At 45° the same two legs carry only 2,828 lb and at 30° 2,000 lb. The calculator's third mode finds the angle for you; if the answer is under 30°, use at least 30° anyway.

What is the included angle at the hook?

For two legs it is the angle between them, 180° − 2θ when θ is each leg's angle from the horizontal. Legs at 60° from the horizontal make a 60° included angle; legs at 30° make 120°. A wide included angle means a low sling angle. Crosby's catalog says to gather the legs of a two-leg sling with an included angle over 90° (a sling angle under 45°), and any sling with three or more legs, in a master link or shackle rather than putting them straight on the hook.

Can I get the angle from the length of the leg?

Yes. If the legs are L long and the hook is H above the attachment points, sin θ = H ÷ L: a 10 ft leg with the hook 7 ft up is 44.4°. If the attachment points are S apart and the legs are symmetric, cos θ = (S ÷ 2) ÷ L: 10 ft legs with the points 12 ft apart are at 53.1°. Choose a longer sling or a spreader beam to raise the angle.

This is a screening tool, not a safety assessment. Lifting accidents kill: use only slings in good condition with a legible tag, have a qualified person plan the rigging, and never stand under a suspended load.

Sources: OSHA, 29 CFR 1910.184 (Slings), paragraphs (b), (c), (f) and (h), and 29 CFR 1926.251 (Rigging equipment for material handling) (eCFR text, read October 27, 2026); The Crosby Group, general catalog, Chain Sling warnings and application instructions (angle measured from the horizontal, a minimum sling angle of 30°, intermediate link for three or more legs); ASME B30.9, Slings (not opened; the 30° rule as quoted in rigging guides). Related: ladder angle calculator, right triangle calculator, NIOSH lifting equation calculator. How we check our calculators.