Estimating Load Weight
Every safe lift starts with one number: how much the load weighs. Overloading a crane, hoist or sling usually happens because someone guessed. If you can’t find the weight, you have to calculate it, and if you can’t do either with confidence, don’t lift.
- Construction
- Rigging
- General Industry
Find the weight first
- Shipping papers, bills of lading and delivery tickets
- Nameplates on equipment, tanks and machinery
- Engineering drawings, steel erection plans and precast shop drawings
- The manufacturer or supplier
- A load cell or crane load indicator during a trial lift
Double-check documents against what you see. Papers can be wrong or list net weight without packaging.
Calculate it: volume × unit weight
Find the volume in cubic feet (length × width × height, all in feet), then multiply by the material’s weight per cubic foot.
| Material | Approximate weight |
|---|---|
| Steel | 490 lb per cubic foot |
| Concrete (reinforced) | 150 lb per cubic foot |
| Aluminum | about 170 lb per cubic foot |
| Water | 62.4 lb per cubic foot (8.34 lb per gallon) |
| Soil, sand and gravel | about 100 to 130 lb per cubic foot, more when wet |
| Wood (lumber) | about 30 to 50 lb per cubic foot, depending on species and moisture |
Use the higher number when you’re unsure. Rigging handbooks and supplier charts list many more materials.
Examples
- Steel plate 10 ft × 4 ft × 1 inch thick: 10 × 4 × (1 ÷ 12) = 3.33 cubic feet × 490 = about 1,630 lb.
- Concrete block 4 ft × 4 ft × 2 ft: 32 cubic feet × 150 = 4,800 lb.
- Hollow shapes like pipe and tanks: find the volume of the outside shape, subtract the inside, and add the weight of any contents.
Don’t forget
- Rigging weight: slings, shackles, spreader bars and below-the-hook devices. See Below-the-Hook Devices
- Crane deductions: the hook block, headache ball and jib, as the load chart requires. See Load Charts
- Contents: water, oil, sludge or product left inside
- Added weight: mud, ice, snow or rainwater
- Attachment: bolts not removed, frozen ground or suction holding the load down
Center of gravity
The center of gravity is the balance point. If the hook isn’t directly over it, the load will tilt or swing when it lifts. Machinery, engines and tanks with contents often have an off-center balance point, sometimes marked on the equipment. Lift a few inches first to check balance. See Rigging Basics.
When you don’t know
- Stop and ask a supervisor, lift planner or engineer.
- Use a load cell or dynamometer to measure it.
- Don’t “test it” by trying to lift and seeing if the crane complains.
Critical lifts, like those near a crane’s capacity, need a written plan with a verified weight. See Lift Planning.
Standards & references
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