How the load weight estimate works
Weight is volume times density. The calculator turns your dimensions into a volume, multiplies by the unit weight of the material, and shows the result three ways:
- Plate and rectangular block: volume = length × width × thickness (or height).
- Round bar and solid cylinder: volume = π ÷ 4 × diameter² × length (or height).
- Pipe: volume = π ÷ 4 × (OD² − ID²) × length, where ID = OD − 2 × wall. That is the steel in the wall only, not what is inside.
- Weight = volume × unit weight. Short tons are pounds ÷ 2,000, and 1 lb = 0.45359237 kg.
- Total to the hook = load + rigging. Slings, shackles, spreader bars and anything else hanging below the hook add to what the crane carries, so enter their weight in the rigging box.
Unit weights used
The densities come from OpenStax University Physics, Table 14.1, and they are typical values, not a spec. Steel uses the table's figure for iron, which is close to common carbon steel.
- Steel: 7,860 kg/m³, about 490.7 lb/ft³ (about 40.9 lb per square foot for each inch of plate thickness)
- Aluminum: 2,700 kg/m³, about 168.6 lb/ft³
- Concrete: 2,400 kg/m³, about 149.8 lb/ft³
- Wood: oak 710 kg/m³ (about 44.3 lb/ft³) and pine 373 kg/m³ (about 23.3 lb/ft³). Wet or green wood weighs more.
Other alloys, rebar in concrete, lightweight mixes and different wood species will differ. Where a code or the maker publishes a weight for the piece, that figure governs, so confirm against it.
Worked example 1: steel plate
A steel plate 10 ft long, 4 ft wide and 1 in thick. Enter 120 × 48 × 1 in. Volume = 5,760 in³ = 3.333 ft³. Weight = 3.333 × 490.7 = 1,636 lb, which is 742 kg or 0.818 short tons. As a check, 40.9 lb per square foot × 40 square feet = 1,636 lb.
Worked example 2: pipe with rigging
One joint of pipe, 12.75 in OD, 0.375 in wall, 20 ft long, in steel. ID = 12.75 − 2 × 0.375 = 12.0 in. Wall area = π ÷ 4 × (12.75² − 12.0²) = 14.58 in². Volume = 14.58 × 240 = 3,499 in³ = 2.025 ft³, so weight = 2.025 × 490.7 = 994 lb. Add 150 lb of slings and shackles and the total at the hook is 1,144 lb, or 0.572 short tons.
These are original arithmetic examples, not exam questions.
Load weight questions
Do I use the calculated weight or the actual weight?
Use the actual weight whenever you have it. It comes from the tag, the mill sheet or shipping paperwork, a load cell or a scale. A calculated weight is a planning estimate for when nothing better is available, and it can be off if the alloy, wall thickness or moisture differ from the typical value.
Do I add the weight of the slings and shackles?
Yes. Everything hanging below the hook counts toward what the crane lifts. Add it here in the rigging box, then check the total against the chart. Your chart's notes say what to deduct for the hook block and other gear, and the net capacity calculator lays that subtraction out one step at a time.
What sling do I need once I know the weight?
Check the load against the sling's tagged rating for the hitch and angle you plan to use. The sling capacity calculator gives capacity by hitch and load per leg, and the sling angle calculator shows how a low angle raises the tension in each leg.
Once you have the total, the crane percent of capacity calculator shows it as a percent of the chart capacity you read.
Working out a load's weight before you rig it is a basic rigging skill, and it comes up in the NCCCO written exams. This tool shows the arithmetic and does not approve a lift.