Sling Tension Calculator (Angle, Legs & Hitch)
Enter the load weight, how many legs carry it and the sling angle measured from horizontal. The calculator returns the tension in each leg, the angle factor behind it, and the inward force the rigging puts on the load. The angle factors and the critical angles are those of OSHA's Advanced Rigging Principles workbook.
Tension in each loaded leg
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Results are estimates for planning purposes and do not replace a competent person's evaluation or an engineer's design. Follow the OSHA standards that apply to your work and your employer's written program.
Sling angle factors
| Sling angle θ | Angle factor |
|---|---|
| 90° | 1.000 |
| 85° | 1.004 |
| 80° | 1.015 |
| 75° | 1.035 |
| 70° | 1.064 |
| 65° | 1.103 |
| 60° | 1.155 |
| 55° | 1.221 |
| 50° | 1.305 |
| 45° | 1.414 |
| 40° | 1.556 |
| 35° | 1.743 |
| 30° | 2.000 |
Critical angles
- 60° — recommended minimum sling angle under ANSI/ASSE A10.48.
- 45° — the A10.48 minimum; below it, special approval is required.
- 30° — the ASME B30.9 minimum; below it, special attention is required. OSHA's angle factor table stops here, with the note “do not set below 30°”.
Listed in OSHA's Advanced Rigging Principles student workbook. Federal OSHA is the floor — your employer's rigging program, the sling manufacturer and, on a critical lift, a qualified person can all require more.
Choker hitch: the angle of choke changes the rating
A choker's rated capacity assumes the sling body bends around the load at more than 120°. Tighter than that and the sling loses capacity — this is a reduction of the rating, not a change in the tension the calculator gives you.
| Angle of choke | Rated capacity |
|---|---|
| Over 120° | 100% |
| 90–120° | 87% |
| 60–89° | 74% |
| 30–59° | 62% |
| 0–29° | 49% |
What this number does not cover
- An off-centre centre of gravity. The calculator assumes the load hangs level with its centre of gravity under the hook. Move it off centre and one leg takes more.
- Unequal leg lengths. The shortest leg takes the load first. This is why three- and four-leg bridles are designed on two legs unless the load is rigid and the legs are matched.
- Shock and dynamic loading. Snatching a load, swinging it or stopping it fast multiplies the tension. 1910.184(c)(9) prohibits shock loading.
- Edges. Slings must be padded or protected from the sharp edges of the load — 1910.184(c)(11), 1926.251(c)(9). A synthetic sling can be cut through in one lift.
- The sling's own condition. Rigging is inspected before use on each shift; damaged or defective slings are removed from service, and a sling without legible identification markings may not be used.
- The crane. Leg tension says nothing about whether the crane can pick the load at that radius. That is the load chart's job.
How it's calculated
- Sling angle factor
AF = 1 / sin(θ)θ is the sling angle measured from horizontal. AF is 1.000 at 90°, 1.155 at 60°, 1.414 at 45° and 2.000 at 30° — the values in OSHA's angle factor table.- Tension in each leg
T = (load ÷ number of legs sharing it) × AFOSHA's workbook states it as Sling Leg Force = (Applied Load ÷ 2) × Angle Factor for symmetrically loaded basket hitches and 2-leg bridle hitches.- Inward force on the load
H = T × cos(θ)The horizontal component each leg applies, squeezing the load inward. It is what crushes thin-walled or unbraced items at low sling angles.- Minimum rated capacity per leg
rated capacity for the hitch used ≥ TCompare T with the rated capacity on the sling's identification marking for the hitch and angle it is based on — 1926.251(c)(16), 1910.184(e)(1), (f)(2).
Frequently asked questions
Because only the vertical part of the leg tension holds the load. At an angle θ from horizontal, the vertical component of each leg is T × sin(θ), so T = (load ÷ legs) ÷ sin(θ). At 30°, sin(30°) = 0.5, so the tension is twice the share of the load the leg is carrying. OSHA's angle factor table gives exactly that: 2.000 at 30°.
OSHA's Advanced Rigging Principles workbook lists three critical angles: 60° is the recommended minimum under ANSI/ASSE A10.48; 45° is the A10.48 minimum, below which special approval is required; and 30° is the minimum under ASME B30.9, below which special attention is required. The workbook's angle factor table stops at 30° with the note “do not set below 30°”.
From horizontal — from the surface of the load. A leg straight up is 90° and has an angle factor of 1.000. Watch out for charts that use the included angle between the two legs instead: a 60° sling angle is a 60° included angle only in the equilateral case, and the two conventions give different numbers.
Only when the load is rigid and the legs are truly the same length and tension. Otherwise the legs do not share equally and two of them can end up carrying everything. Standard rigging practice, and the default of this calculator, is to assume two legs carry the load on a three- or four-leg bridle. Notice that OSHA's own workbook gives the sling force formula for symmetrically loaded basket hitches and two-leg bridles only.
It changes the capacity, not the arithmetic of a single vertical leg. A choker's rated capacity depends on the angle of choke: OSHA's Fig. 2 gives 100% of the choker rating over 120°, 87% at 90–120°, 74% at 60–89°, 62% at 30–59° and 49% at 0–29°. Chokers also grip rather than support, so the rating on the tag is already lower than the same sling's vertical rating.
Not by guessing. Use the shipping documents, the nameplate, a load cell or a scale, or a documented calculation from dimensions and material — that is what the load weight estimator on this site is for. Every number below is only as good as the weight you put in, and an underestimated load is the most common cause of rigging failure.
The rated capacity for the hitch actually used, at the angle the rating is based on. OSHA requires that identification marking: 1926.251(c)(16) and 1910.184(f)(2) for wire rope, (e)(1) for alloy chain. A sling with no legible marking may not be used, and slings may never be loaded above their rated capacities.
No. It gives leg tension for a symmetric lift with the load's centre of gravity under the hook. It does not deal with an off-centre centre of gravity, unequal leg lengths, spreader bars, dynamic or shock loading, sling-to-edge protection, or the crane's own capacity chart. Critical or engineered lifts need a qualified person and a written plan.
Sources & references
- OSHA — Advanced Rigging Principles Training Course, Student Workbook: sling forces, sling angle factor table, critical angles (60° per ANSI/ASSE A10.48, 45° minimum, 30° per ASME B30.9)
- OSHA — Guidance on Safe Sling Use, Tables and Figures: Fig. 2 angle of choke and the rated capacity reduction it causes
- 29 CFR 1926.251 — Rigging equipment for material handling: inspection each shift, identification markings, rated capacity for the hitch and the angle it is based on
- 29 CFR 1910.184 — Slings: safe operating practices, angle of loading definition, identification markings, no loading above rated capacity, no shock loading
- ASME B30.9 — Slings (paid consensus standard; named here, not reproduced). It is the source of the 30° minimum sling angle cited in OSHA's rigging workbook.
Content checked against these sources — last reviewed August 27, 2026.