Screw Conveyor Calculator

The engine first solves for the RPM required to hit your target throughput, then compares that against a CEMA speed ceiling of roughly 60/√(diameter in inches / 12) for your screw diameter, following the maximum recommended speed guidance in ANSI/CEMA Standard No. 350. If the required RPM exceeds that ceiling, the calculator caps the speed there instead of letting it run faster, then reports the actual (lower) throughput you'd get at the capped speed — spinning a screw past its recommended limit accelerates wear and material degradation without adding much real capacity.

The engine applies a quadratic reduction factor, 1 − 0.015 × angle − 0.0003 × angle², floored at 0.25 so capacity never drops below 25% of horizontal. That means loss accelerates as the angle climbs: a modest 10° incline only costs a small fraction of throughput, but by 45° you're retaining just the floor value — a 75% loss — which is why steep incline runs are usually redesigned as steeper, shorter screws or replaced with bucket elevators.

The friction-power term uses a screw diameter factor, Fd = 20 + 0.2 × diameter (mm), that grows linearly with bore size, so a bigger screw carries more inherent friction load even before you factor in material weight. Combined with the fact that a larger diameter also lets you run fewer RPM for the same throughput, the net power change depends on both effects together — this calculator's power output already accounts for that trade-off for your specific inputs.

No — the material factor Ff is fixed at 1.0 in this calculator, which represents a free-flowing material like grain or dry sand. Abrasive materials (like sand with sharp particles) or sticky, high-friction materials can require Ff values up to roughly 4.0 in the full CEMA 350 method, so the motor power and torque shown here should be treated as a minimum for anything other than free-flowing material.

Pitch ratio sets pitch as a multiple of screw diameter — 1.0 is standard pitch (pitch equals diameter) and 0.67 is short pitch. Since volume moved per revolution scales directly with pitch, a short-pitch screw moves less material per turn at the same RPM, but the tighter helix gives better control of material on inclines and in vertical or near-vertical applications where standard pitch would let material slip backward between flights.