Lifting operations · Symmetric two-leg model
Calculate equal two-leg sling tension using the horizontal angle
Estimate tension in each of two equal sling legs, with the angle measured from horizontal.
By HSECalc · Published
Check that this method fits your task
Two equal legs, centred centre of gravity and a static load only. Not a lifting-plan approval or a calculation for unequal legs, shock loads, choker/basket ratings or multi-leg load sharing.
Choose your inputs and work through the steps
- Confirm a centred centre of gravity, equal angles and static load sharing. Unequal arrangements need a different analysis.
- Enter the total supported load force in kN and the leg angle above horizontal. A vertical leg is 90° in this tool.
- Enter the verified applicable capacity per leg for the actual configuration. Compare static tension with that entered capacity, then have the complete lift arrangement checked.
Tension per leg = total load force / (2 × sin(angle above horizontal)). This version accepts 30° to 90° only.
A worked example
Illustrative values explain the tool; they are not prescribed inputs for your work.
- Total force 20 kN, angle 30°: sin(30°) = 0.5.
- Tension per leg = 20 ÷ (2 × 0.5) = 20 kN.
- Against an entered 15 kN per-leg capacity, the static result is overloaded. Do not proceed on that arrangement.
Read the result and decide what needs checking
Lower angles increase leg tension. This tool accepts only 30°–90° and cannot account for shock, snagging, unequal sharing or every rigging configuration.
Mass in kilograms is not force in kN. Use the load force and allowances established by the lifting planner; do not simply copy a mass value into the force field.
Common questions
Is the angle from vertical?
No. Enter the angle above a horizontal line. A vertical leg is 90° in this calculator.
Can I enter kg as kN?
No. Kilograms are mass, kN is force. Have the lifting planner establish the design load force and relevant allowances.
Does an amber result allow the lift?
No. Even when static tension is within the entered capacity, the complete arrangement needs competent verification.
References and scope notes
Use the current official guidance and the instructions for your actual equipment. HSECalc is independent; a reference is not an endorsement. Read how we use methods and sources or report a correction.