Always consider the sling angle when making a lift. The angle of the sling can reduce the capacity of all the rigging due to sling tension. As an example, a horizontal sling angle of 30° will increase the tension factor by 2 times therefore doubling the weight felt by the sling and all related rigging. You can use the chart below to calculate tension factors. If appropriate overhead clearance is available, most riggers us a 60° triangle as a benchmark angle. A 60° triangle has three equal sides making it a quick and easy reference point for estimating your sling angle. If a more critical assessment of the sling angle is necessary, the information below can assist in more precise angle calculations. Calculations should always be verified by a qualified person.
Example:
Vertical choker rating each sling  6000 lbs.
Measured Length (L) = 6 ft.
Measured Height (H)= 4 ft.
Reduction Factor (RF) 4(H) ÷ 6(L) = .667
Reduced sling rating in configuration = .667
(RF) x 6,000 lbs. = 4,000 lbs. of lifting
capacity per sling
Example:
Load weight = 1000 lbs.
Rigging  2 slings in vertical hitch
Lifting
Weight (LW) per sling  500 lbs.
Measured Length (l)  10 ft.
Measured Height (h)  5 ft.
Tension Factor (TF)= 10(L)
÷ 5(h)= 2.0
Minimum Vertical Rated Capacity required for this lift = 500(LW) x 2.0(TF) = 1000 lbs. per sling
STEPS TO CONSIDER WHEN CALUCLATING SLING ANGLES
1.Calculate the Reduction Factor (RF)
a. Using the angle from horizontal, read across the Angle Chart to the corresponding number of the Reduction Factor column.
 OR 
b. Divide sling height* (H) by sling Length* (L).
2. Reduction Factor (RF) x the sling's rated capacity for the type hitch that will be used  Sling's Reduced Rating.
STEPS TO DETERMINE NECESSARY SLING CAPACITY
1. Determine the weight that the sling will be lifting (LW)
2. Calculate the Tension factor (TF).
a. Using the angle from horizontal, read across the angle chart to the corresponding number of Tension Factor column
b. Divide sling length*(L) by sling height*(H)
 OR

3.Lifting Weight (LW) x the Tension Factor (TF)= Minimum Sling Rating for the type of hitch that will be used.
*Measured from a common horizontal plane to the hoisting hook.
* Rated capacities of choker hitches apply when angle or choke is greater than 120°