If you're working with a load that has a different load center than the forklift rating on the data plate (usually 24") and you are using a counterbalanced forklift, the basic formula is:

Moment(Center of Drive Axle Moment)                                                    Center of wheel to fork face + Load Center = Capacity

Example:

Hyster S30XM is a 3,000 lb capacity forklift at a 24" load center. Let's say you want to pick up a uniform 8' long load (48" load center). The manufacturer's stated moment is 114,300 in. lb.

114,300/(14.1+48)=1840 lbs capacity

Since several factors such as high lift masts, sideshift attachments, wide tread designs and others may effect actual capacity, contact the forklift dealer or manufacturer for specific requirements.