One of the most common mistakes people make when buying lifting equipment is working backwards from a product rather than forwards from a requirement. They find the suitable equipment and then think about its lifting capacity, checking if the equipment can lift about the desired load weight. This seems to be logical but usually leads to buying equipment that is either oversized or undersized.

At Lifting Hoists Direct we talk to many customers who deal with the same problem. This guide explains how to calculate load capacity needed.

Start with Calculating the Exact Load Weight

The first step is the calculation of the gross weight of your load. Not estimated weight, but the exact load weight. In case your load consists of different parts (a pallet with materials plus the pallet itself or the load plus its rigging tackle) the weight of all these components should be included. It is also necessary to understand that dynamic forces may increase the weight of the load.

Know What Working Load Limit is and Why It Is Different from Breaking Load

Each hoisting equipment has its Working Load Limit (WLL) that is the maximum load weight it can handle. It is important to understand that this load weight is not the weight at which the equipment fails – breaking load weight is always higher. SWL is the weight limit calculated considering wear and tear and other variables that cannot be calculated in the lab conditions.

The Working Load should always be equal or exceed the load weight of the equipment. Using the equipment exceeding SWL is both unsafe and illegal according to LOLER.

Calculate Your Equipment with Margin

In industrial operations experienced people usually do not simply match their SWL and load weight. They always have some margin. For example, if the operating environment is very demanding, if the load is dynamically increased or if the equipment will be used intensively, choosing the hoist with greater maximum weight of the load gives a possibility to have additional margin and to prolong the lifetime of the equipment.

A standard procedure in this case is as follows: if the load weight equals 1 tonne, choose the equipment able to operate with the maximum load weight 1.5 or 2 tonnes depending on your requirements.

Consider Rigging Configuration

If you are going to use some slings or chains for rigging, the angle of these rigging elements is very important – it determines the load weight on each leg of the rigging equipment. Rigging equipment lifting a load vertically distributes the load weight equally, but as the angle between multi-leg slings increases, the load weight on each leg also increases significantly.

It is very important factor that is often omitted. The SWL of slings and other rigging tackle should be calculated having in mind the rigging angle of the load, as well as the type of hitch used; not just the load weight itself.

Consider Headroom, Lift Height and Operating Frequency

Of course, the main factor that influences the choice of the equipment is its load capacity. However, there are other factors as well: how much headroom is available between the load and the mounting point of the equipment? At what height should the load be lifted? At what frequency will the operation take place – once a week or several times per day? All these factors will influence the type of the equipment and the model of this equipment that is the best fit for your case.

When in Doubt – Discuss It with Us

Calculating the load capacity of the equipment is simple once you know the formula, but calculating the combination of load weight, SWL, rigging angle and other factors is not so easy. If you are not sure about your calculations, our specialists will help you to calculate everything and to buy the best equipment for you.