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How is the Size (Tonnage) of a Crane Determined

17 Ton Chart

17 Ton Chart

275 Ton Chart

275 Ton Chart

For those of you that already know how the tonnage of a crane is calculated, this may come as an amusing surprise – but we get calls in all the time from well meaning contractors asking for our 17 ton crane (our smallest) because they have to lift 34,000 pounds.  The problem is that their radius (horizontal distance from center of crane to center of load) is 100′!  In this case the pick requires my 275 ton crane…the largest in the fleet!

The size of a crane can be confusing and perhaps misleading if you are unaware of how the manufacturers rate their machines.  In general, a cranes tonnage rating is determined by how much weight it can pick approximately 5′ away from it’s center pin.  But as you go further away from that point the capacity of the crane decreases.  Additionally, the higher you have to lift a piece, the more boom must be pushed out, also reducing capacity.

The capacity of a crane is variable, based on many factors.  More then likely, a crane, once it leaves the factory, will never pick the amount of weight it is rated for.

In our situation above, our 17 on can lift 34,000 lbs 4.5′ away from it’s center pin (see 17 Ton Chart).  But as you go further out  (follow chart down) 8, 10 , 12, 14 feet, the capacity is greatly reduced.  The furthest the 17 can go out from it’s center pin is 80′.  And at that distance the crane can only support 650 lbs.