CEMA calculates capacity using the cross-sectional area between the screw outer diameter (D) and center pipe (d), multiplied by screw pitch (P), rotational speed (RPM), and percent trough loading (15%, 30%, 45%, or 95%). For standard full-pitch screws (pitch = diameter), capacity at 1 RPM is multiplied by actual speed and the incline correction factor (Fi).

As a screw conveyor inclines upward, bulk material tends to roll backward under gravity over the rotating center pipe rather than being pushed forward. At a 10° incline, capacity drops by 20% (Fi = 0.80); at 20°, capacity drops by 40% (Fi = 0.60). Inclines steeper than 15° require short-pitch flights (2/3 standard pitch) or tubular housings to maintain conveying efficiency.

Friction Horsepower (HPf) represents the mechanical power needed to rotate the empty screw against hanger bearing and seal friction. Material Horsepower (HPm) represents the work done pushing and tumbling the bulk solid along the trough, which depends directly on material throughput (lb/hr), conveyor length, and the CEMA material factor (Fm).

CEMA designates 15% loading for heavy, abrasive, and sluggish materials (sand, clinker, iron ore) to keep material level below the hanger bearings and minimize wear. 30% loading applies to medium-weight, mildly abrasive materials (coal, cement, limestone). 45% loading is reserved strictly for light, non-abrasive, free-flowing solids (grains, flour, seeds, wood pellets).

At low operating horsepowers (under 5 HP), mechanical friction and starting inertia can be disproportionately high, especially during cold starts or when restarting under a full head of consolidated material. CEMA specifies overload multipliers up to Fo = 2.0 for fractional horsepowers to provide adequate breakaway starting torque without motor overheating.