A forklift's data plate gives its rated capacity Q at a stated load centre c0, typically 500 mm or 600 mm from the fork face, and at a stated lift height. Move the load's centre of gravity further out, or lift higher, and the capacity falls.
Load centre
A counterbalance truck tips about its front axle. Capacity therefore follows the load moment about that axle. With x the distance from the front axle to the fork face and X the actual distance from the fork face to the load's centre of gravity:
C = Q × (x + c0) ÷ (x + X)
Example: Q = 3,000 kg at c0 = 500 mm, x = 450 mm, and a load whose COG is 800 mm from the fork face. C = 3,000 × 950 ÷ 1,250 = 2,280 kg. If the plan applies a 90 % duty limit, the load must not exceed about 2,050 kg.
Lift height and mast
Manufacturers publish capacity tables by mast type and lift height. Read the row at or above the planned lift height; never interpolate below it. Attachments such as fork extensions and side shifters reduce capacity further and change the load centre.
Several loads on the forks
When several items are carried together, find their combined centre of gravity measured from the fork face: X = Σ(W × x) ÷ ΣW, where x is each item's own COG distance from the fork face. Then use X in the capacity formula.
Always check
- The data plate on the truck actually being used.
- Ground: slopes, soft ground and potholes reduce stability.
- Travel with the load low and tilted back; never raise or lower while moving.
The forklift lift planner holds 915 trucks from 34 makers, applies these derating steps and checks single loads, multiple loads and tubular bundles.
General guidance only. It does not replace the manufacturer's data, the applicable standards or the judgement of a competent person.