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General rigging principles
Weight of the load
Understand how the weight of a load affects the way it can be lifted.
To select the correct lifting equipment, verify the weight and Centre of Gravity (CoG) of the load.
Do not lift if the weight of a load is unknown. The load weight may be:
- marked on the load
- on the delivery docket
- on the weighbridge certificate
- verified by a manufacturer.
How to calculate the weight of a load
It is also possible to calculate the weight of a load. Once you know the mass of a load, you can select the correct sling.
To calculate the weight of a load if it is unknown: multiply the volume of the load by the unit of weight of the load.
Here's an example:
How to calculate the weight of a load
A rectangle stack of hard wood 3 metres long, 1 metre high and 1 metre across.
To get the volume of a rectangle solid:
Length x width x height
In this example:
3 x 1 x 1 = 3 cubic metres
The unit weight of hardwood is 1120kgs per cubic metre, as per the chart below.
Calculate: 3 x 1120kgs = 3360kgs
| Material | Weight per cubic metre (unless specified) |
|---|---|
| Aluminium | 2.7t |
| Ashes, coal | 800kg |
| Brass | 8.5t |
| Bronze | 8.5t |
| Cast iron | 7.2t |
| Cast steel | 7.9t |
| Cement, one bag | 20kg (0.02 cubic metres) |
| Cement, 50 bags | 1t |
| Coal | 860kg |
| Concrete | 2.4t |
| Copper | 9.0t |
| Copper, 3mm thick, square metre | 27kg |
| Cotton bale | 250kg |
| Drums, empty 200 litre (44 gallons) | 13kg |
| Earth | 1.9t |
| Fibrous plaster, square metre | 1.6kg |
| Fibre board, square metre | 0.6kg |
| Ice | 930kg |
| Iron, cast | 7.25t |
| 100mm pipe | 28kg/m |
| 150mm pipe | 54kg/m |
| 200mm pipe | 84kg/m |
| 225mm pipe | 100kg/m |
| 250mm pipe | 115kg/m |
| 300mm pipe | 148kg/m |
| Timber, ironbark | 1.4t |
| Timber, other hardwoods | 1.12t |
| Tubular scaffolding (1.5in bore) 48mm O.D 4.8mm thick | 5.2kg/m |
Cubic metre weight chart
An example of how to confirm the load weight is to perform a test lift. A test lift may confirm that the weight and Centre of Gravity of the load is within the crane's rated capacity.
Always "float the load" just off the ground to check its balance before lifting.
If the load is unbalanced:
- lower back to the ground
- readjust slings
- check balance again.
How different factors affect the weight of a load
Many factors can affect the weight of materials. Here are some examples:
- timber can be 50% heavier when wet
- when loads are raised from a mould, there can be suction created by the sand, wet muddy conditions and wet moulds. Suction can mean more force is needed to release the load from the mould. Be aware of potential uncontrolled movement upon release.
- pipes, tanks, motors, gearboxes and compressors could be weighed down by residual liquids, sludge or other materials
- the weight of concrete can vary due to moisture content, suction and internal reinforcement.
Formula for calculating the volume of different shaped objects:
Volume: units of measurement