Total suspended and design load
The dynamic amplification factor and additional design factor are user inputs. They must come from the lift procedure, engineering basis, equipment instructions, or applicable rules.
Equal-leg bridle tension
Here, T is the ideal tension in each active leg. The term n is the assumed number of load-bearing legs. The angle θ is measured from horizontal.
Angle conversions
Force components
Effective sling capacity
Two-support center-of-gravity reactions
The four-point calculation applies these shares in both orthogonal directions. This creates a bilinear rectangular-support estimate.
Simplified beam actions
These equations represent simplified preliminary cases. Actual lifting beams and spreader beams require verification of member strength, buckling, lugs, welds, pins, local stresses, deflection, stability, and load combinations.
Block-and-tackle line pull
Tandem-crane static share
This is only a static two-support estimate. Real tandem lifts can transfer load as booms deflect, radii change, hoist speeds differ, or the load rotates.
Prepare verified lift information first
Confirm the actual load weight, dimensions, center of gravity, lifting points, sling identification, hardware markings, inspection condition, crane data, and site restrictions. A drawing or manufacturer document is preferable to an estimate.
Choose the closest calculation mode
Select a vertical lift, bridle, basket, choker, beam, block system, asymmetrical arrangement, or tandem-crane estimate. The selected mode controls which special result panels are displayed. The core sling calculation still uses the entered active-leg count and geometry.
Enter all suspended weight
Do not enter only the payload. Include slings, shackles, master links, lifting beams, frames, clamps, baskets, and other below-the-hook equipment. Include a hook block only when the project method treats it as part of the relevant suspended design load.
Set the sling geometry carefully
Identify whether the known angle is measured from horizontal, vertical, or between opposite legs. A common source of serious error is using the correct number with the wrong reference. Review the converted horizontal, vertical, and included angles after calculation.
Use conservative active-leg assumptions
Three- and four-leg assemblies may not share load equally. Sling length tolerances, a rigid load, an offset center of gravity, unequal lift-point elevations, and hook position can place more load into one leg. Enter only the number of legs that the approved method permits you to count.
Enter manufacturer-supported capacities
Use the identification tag, certificate, manufacturer chart, or approved equipment register. Do not estimate a working load limit from sling color, diameter, or appearance unless the manufacturer documentation explicitly supports that method.
Apply documented capacity factors
The hitch and derating section multiplies the tagged capacity. Enter a factor below one only when supported by documented guidance. The calculator intentionally does not invent temperature, edge, D/d, chemical, side-load, or wear reductions.
Check the entire load path
Enter major hardware items. The master link and crane hook are compared with total design load. Load shackles and lifting lugs are compared with an ideal leg tension. Change the entered factor when a documented angular or side-load reduction applies.
Review center-of-gravity reactions
Enter the center-of-gravity coordinates relative to the support rectangle. Check for highly unequal or negative reactions. A negative reaction means the simplified support polygon does not contain the entered center of gravity.
Read warnings before accepting any result
A pass status means only that calculated demands are below the capacities entered into this page. It does not certify the equipment, the rigging arrangement, the crane setup, the lifting points, or the complete operation.
Export the calculation record
Use the print command to create a PDF through the browser. Use CSV for a tabular record. Add project notes describing the communication plan, exclusion zone, edge protection, environmental limits, landing area, and lift-control method.
The table shows the ideal tension multiplier per leg for a symmetrical two-leg bridle. The multiplier is applied to the total design load.
| Angle from horizontal | Angle from vertical | Included angle | Tension per leg as fraction of load | Approximate increase versus 90° |
|---|---|---|---|---|
| 90° | 0° | 0° | 0.5000 × total load | 0.0% |
| 75° | 15° | 30° | 0.5176 × total load | 3.5% |
| 60° | 30° | 60° | 0.5774 × total load | 15.5% |
| 50° | 40° | 80° | 0.6527 × total load | 30.5% |
| 45° | 45° | 90° | 0.7071 × total load | 41.4% |
| 40° | 50° | 100° | 0.7779 × total load | 55.6% |
| 35° | 55° | 110° | 0.8717 × total load | 74.3% |
| 30° | 60° | 120° | 1.0000 × total load | 100.0% |
| 25° | 65° | 130° | 1.1831 × total load | 136.6% |
| 20° | 70° | 140° | 1.4619 × total load | 192.4% |
| 15° | 75° | 150° | 1.9319 × total load | 286.4% |
| 10° | 80° | 160° | 2.8794 × total load | 475.9% |
The table is mathematical only. It does not establish a permissible minimum angle or rated capacity for any sling.
A larger installation can connect this calculator to an equipment database. Recommended fields are listed below.
Identity and ownership
Capacity and geometry
Inspection and certification
Condition and restrictions
Audit and revision
Idealized load sharing
The primary sling formula assumes identical geometry and equal load sharing between active legs. Real assemblies can develop unequal forces because of sling stretch, fabrication tolerance, load stiffness, lift-point elevation, hook eccentricity, and three-dimensional geometry.
No automatic certification
The software cannot inspect equipment, validate tags, authenticate certificates, determine material condition, approve repairs, or confirm that a selected component is compatible with its connection.
No crane-chart calculation
The tandem mode compares estimated static shares with capacities entered by the user. It does not calculate crane radius, boom configuration, reeving limits, outrigger reactions, ground bearing pressure, wind limits, or chart deductions.
No lifting-point structural design
The lifting-lug line checks only an entered WLL. It does not analyze plate bending, tear-out, bearing, welds, pin bending, cheek plates, local shell stresses, or load direction.
Simplified beam analysis
The beam mode does not check lateral stability, elastic or inelastic buckling, combined axial and bending stress, weld groups, lug design, fatigue, proof testing, or code-specific resistance factors.
No shock-load prediction
Dynamic behavior depends on hoist acceleration, slack removal, load snagging, crane motion, vessel movement, wind, load flexibility, and control actions. A single dynamic factor is only a planning input.
No personnel-lifting approval
Personnel lifting is outside the scope of a generic calculator. It normally requires dedicated equipment, special procedures, additional factors, and strict regulatory controls.
Manufacturer data controls
When this calculator conflicts with the equipment tag, certificate, manufacturer instructions, engineered procedure, or governing rule, stop and resolve the discrepancy before lifting.
Why does sling tension increase at a low angle?
A flatter sling must develop a larger total force to provide the same vertical support. The horizontal force also increases, which can create significant inward loading at lifting points.
Should four sling legs always be counted?
No. Equal sharing depends on geometry, flexibility, tolerances, and the approved method. Use the active-leg count allowed by the qualified person or governing procedure.
What is total suspended load?
It is the payload plus all relevant rigging and below-the-hook equipment. Omitting beam, frame, clamp, sling, or hardware weight understates the design demand.
Does a basket hitch always double capacity?
No universal assumption should replace the sling tag and manufacturer table. Bend diameter, load shape, contact, edge condition, balance, and connection geometry may change usable capacity.
Can this calculator choose a shackle size?
It can compare demand with an entered WLL. Final selection must consider pin diameter, bow space, side loading, multi-leg connection, thread engagement, compatibility, and manufacturer instructions.
What does a negative lifting-point reaction mean?
It indicates that the entered center of gravity lies outside the simplified support polygon. One point would need tension in the opposite direction, so the assumed support arrangement is unstable.
Can I use estimated load weight?
Only when the approved planning process permits it and adds suitable conservatism. Critical lifts normally require a traceable and verified load weight.
Does a pass result approve the lift?
No. It only means the mathematical demands are below the values entered. It does not approve the crane, ground, equipment condition, rigging method, or worksite controls.
How should center of gravity be entered?
Use a consistent plan-view origin. Enter X and Y coordinates from the same reference edges used for the lift-point spans and hook position.
Why is the hook position important?
The hook should generally align with the center of gravity for a level lift. An offset can cause tilt, load shift, and unequal sling forces.
Can the beam result be used for fabrication?
No. The beam equations are preliminary. Fabrication requires a complete engineered design, materials, weld details, lugs, stability checks, inspection, and testing requirements.
How is pulley efficiency handled?
The calculator raises the per-sheave efficiency to the number of sheaves. It then multiplies that result by the supporting rope parts.