Center of Gravity Calculator: Rigging CG Location for Lifting

How It Works

1. Select Calculation Mode

   Choose simple beam mode for 2-point weighing of a single object, or composite body mode for loads made up of multiple components at different positions.

2. Enter Component Data

   For simple beam mode, input the total weight and reaction forces at two known support points. For composite body mode, input the weight and x/y/z coordinates of each component's individual center of gravity (up to 10 components).

3. Calculate Overall CG

   The calculator applies the weighted average formula x_cg = Sum(mi x xi) / Sum(mi) for each axis to determine the overall center of gravity location in 3D space.

4. Review Diagram and Rigging Guidance

   An SVG diagram shows the CG location relative to the load outline and planned pick points. The calculator identifies whether the CG is centered between pick points or offset, and provides sling length adjustment guidance.

Built For

• Riggers locating the CG of a pump skid with motor, baseplate, and coupling before a tandem crane pick
• Lift planners calculating CG offset on an asymmetric structural steel assembly to determine sling length adjustments
• Millwrights using the 2-point weighing method with crane scales to verify CG on a 25,000 lb heat exchanger
• Ironworkers figuring the balance point of a bridge girder with variable flange thickness along its length
• Mechanical contractors locating CG on a rooftop air handling unit with internal components at different heights
• Shipyard workers calculating CG of fabricated hull sections with internal stiffeners and attached piping
• Training instructors teaching rigging apprentices how CG location affects load behavior during a crane pick

Features & Capabilities

2-Point Weighing Mode

Enter scale readings at two support points and the distance between them. Calculates CG position along the beam axis using the moment balance equation.

Composite Body Mode

Enter up to 10 components with individual weights and x/y/z coordinates. Calculates the combined CG using the weighted average formula for each axis.

Negative Weight (Void) Support

Enter negative weight values for cutouts or voids in the load. The calculator subtracts their moment contribution to shift the CG correctly.

SVG CG Diagram

Generates a visual diagram showing the calculated CG position relative to the load outline and pick point locations.

Tipping Analysis

Checks if the CG falls within the pick point envelope. Flags configurations where the load will tilt or become unstable during the lift.

PDF Export

Export CG calculations and diagrams as a branded PDF for lift plans, engineering submittals, and safety documentation.

Assumptions

• CG calculated using weighted average: x_cg = Sum(mi x xi) / Sum(mi) for each axis — standard first-moment method.
• Component weights and centroid positions are known and entered accurately — errors in input propagate directly to CG error.
• Each component is treated as a point mass at its centroid — internal mass distribution within a component is not modeled.
• 2-point weighing method assumes rigid-body behavior: the load does not deflect significantly between support points.
• Negative weight entries (voids/cutouts) assume the void is fully empty — partially filled cavities require manual weight adjustment.

Limitations

• Does not account for hidden internal mass (concrete fill, trapped liquids, internal piping, electrical conduit) that is not visible from the outside.
• Composite body mode limited to 10 components — complex assemblies with more components require consolidation of subassemblies.
• Does not perform stability analysis for the lifted load — only locates the CG position without evaluating whether the load will rotate during lifting.
• Does not model CG shift from liquid sloshing in partially filled tanks or vessels during the lift.
• Accuracy depends entirely on input quality — field verification via 2-point weighing or trial lift is recommended for critical picks.

References

• ASME BTH-1 — Design of Below-the-Hook Lifting Devices (CG location and load stability requirements for lifting device design).
• ASME B30.20 — Below-the-Hook Lifting Devices: Safety Standard (design, proof testing, and marking requirements).
• Shapiro, Howard I. — Cranes and Derricks (4th Edition) — rigging engineering including CG determination and load stability.
• Crosby Group Rigging Handbook — field CG estimation methods and 2-point weighing procedures.
• OSHA Technical Manual Section V Chapter 4 — Crane Safety (load CG considerations for crane operations).

Frequently Asked Questions