Sling angle and tension calculator
Each leg's vertical rated load must be at least this.
Tension per leg for this load at common angles, 2 legs carrying
| Angle | LAF | Per leg |
|---|---|---|
| 90° (vertical) | 1.000 | 5,000 lb |
| 60° | 1.155 | 5,774 lb |
| 50° | 1.305 | 6,527 lb |
| 45° | 1.414 | 7,071 lb |
| 30° | 2.000 | 10,000 lb |
Formulas and sources
- Load angle factor = L ÷ H = 1 ÷ sin(horizontal angle)
- Tension per leg = (load ÷ legs carrying) × load angle factor
The formula comes from
U.S. DOE, Hoisting & Rigging Fundamentals (TR244C), Load Angle Factor (LAF) and Sling Tension(opens ecfr.gov in a new tab)“Step 1: Determine load designated to pick point. Step 2: Measure the sling length. Step 3: Measure the vertical height from the horizontal plane of the load to the point where the sling attaches to the suspended hook. Step 4: Divide the sling length by the vertical height. The result is the "Load Angle Factor" (LAF). Step 5: Multiply the LAF times the portion of the weight designated to that particular pick point. The result is the total stress load applied to that particular sling.”
The formula comes from
DOE-STD-1090-2004, Hoisting and Rigging, 11.3.1.1 Load Angle Factor(opens ecfr.gov in a new tab)“1. Load = 1,000 lb. 2. Sling = 2-legged bridle. 3. Angle with horizontal = 45 degrees. 4. Load angle factor from Figure 11-7 = 1.414. b. Each of the two legs would lift 500 lb if a vertical lift were made. However, there is a 45 sling angle involved. Therefore, the 500-lb load would be multiplied by the load-angle factor in the chart, giving a total of 707 lb (500 lb x 1.414) tension in each sling leg. Each sling leg, therefore, must have a rated capacity of at least 707 lb.”
Source
DOE-STD-1090-2004, Hoisting and Rigging, 11.3.1.2 Safe Load(opens ecfr.gov in a new tab)“Two legs should be considered to carry the load because in normal lifting practice, the load will not be uniformly distributed on all legs. If rigging techniques, verified by a qualified rigger, ensure that the load is evenly distributed then full use of three legs is allowed. Special rigging techniques verified by a member of a qualified engineering organization shall be required to prove that a load is evenly distributed over four or more sling legs.”
Source
OSHA, Guidance on Safe Sling Use: Tables and Figures, Fig. 5 (Hitch Types for Synthetic Rope Slings)(opens ecfr.gov in a new tab)“GENERAL NOTE: Legs 5 deg or less from vertical may be considered vertical. Slings with horizontal angles less than 30 deg should not be used.”
FAQ
What is the sling tension formula?
Tension in each leg = (load ÷ number of legs carrying it) × load angle factor. DOE-STD-1090's example: a 1,000 lb load on a 2-leg bridle at 45° puts 500 × 1.414 = 707 lb in each leg, so each leg must be rated for at least 707 lb.
How do you find the load angle factor?
Divide the sling length (L) by the vertical height (H) from the load's pick points to the hook. That ratio equals 1 ÷ sin of the horizontal sling angle: 1.000 at 90°, 1.155 at 60°, 1.414 at 45° and 2.000 at 30°.
Why does a lower sling angle increase tension?
Only the vertical part of each leg's pull holds up the load. As the angle from horizontal gets smaller, each leg has to pull harder to supply the same vertical force, so tension rises even though the load hasn't changed.
What is the minimum sling angle?
OSHA's Guidance on Safe Sling Use says slings with horizontal angles less than 30° should not be used. At 30° each leg already carries twice its vertical share.
How many legs carry the load on a 3- or 4-leg bridle?
Assume two. DOE-STD-1090 says two legs should be considered to carry the load because it won't be evenly shared in normal practice, unless a qualified rigger (3 legs) or a qualified engineering organization (4 or more) verifies even loading.
The sin form matches OSHA's published sling tables: a Grade 80 chain bridle at 60°, 45° and 30° is rated at about 2 × the single-leg vertical rating × sin(angle). For chokers, see the angle-of-choke reductions on the free CHST formula sheet. Equal legs and a centered load are assumed. This tool is for study and planning, not a substitute for a qualified rigger or a lift plan.