A colleague gave me the following equation to calculate torque on a conveyor for use in spec'ing a gearbox. (Belt weight + product weight) x gravity x Friction x Sprocket Radius = Nm (30kg + 1kg) x 10 x 0.3 x 0.13m = 6Nm Which seems really small, am I doing something wrong here?

Did you ever get an answer to this? If not then there is an arithmetic error here. You have 31 x 10 = 310x0.3=93x0.13=12.09NM.

The torque will depend on the capacity of the conveyor in TPH, the length of the conveyor, the belt speed in m/sec, The rise in the conveyor in meters.. From these inputs the power at Conveyor shaft is calculated.and depending on driven drum radius the torque is arrived at.