# Lifting Capacity of Crane

Undestand here how to decide the lifting capacity of crane and how to read the working radius/lift height diagram written in any crane specifications sheet.

- Elements to decide lifting capacity

The following three factors decide the lifting capacity

- Crane strength (whether or not crane breaks)
- Crane stability (whetever or not crane overturns)
- Winch capacity (whetever or not the winch can wind up)

Crane’s lifting capacity is decided by the smallest among these three elements.

Total rated loads are based on crane stability when working radius is big, but on the strength of the boom and others, when working radius is small

To calculate crane strength under officialregulation, such things are taken into consideration as only the total rated load but crane’s weight, inertia force and centrifugal force due crane’s swing, boom elevation and win force.

- Crane stability

Crane with load can be compared to a steelyard as in the figure below. Since G x l is decided by the scale of the crane, W will be smaller as l1 increases

G x l > W x l1 …………….. stable

G x l < W x l1 …………….. Overtuning

**How to See Total Rated Loads Chart and working radius/Lifting Heigth Diagram**

** **

- Total rated loads charts

This chart gives the total rated based on working conditions such as boom length, jib length, offsets angle, working radius etc. Such charts can always be found in the crane operator’s cab.