Johnr-j is correct in his advice.

However if you are only going to carry the load at a low height - that is much lower than the maximum lift of the mast - then the formula is as follows:

Rated load x (rated distance plus the distance from the fork face to the centre of the drive axle) = modified rating x (modified distance plus the distance from the fork face to the centre of the drive axle).

For example a 2000 kg @ 24 in forklift plus 16 in from fork face to centre of drive axle would have a revised rating of 2000 x (24 + 16) = revised rating x ( 78 + 16) giving a rating of 850 kg.

Note that this revised rating includes the effect of the carpet prong on stability. Assuming the prong is supported on the forks, and the prong weighs 100 kg then conservatively the device can carry a roll of carpet 850 - 100 = 750 kg.

It is still recommended that the manufacturer be contacted re a new rating as they can give the rating at full mast height.