How is this different from the old factor?

The old page multiplied a load in pounds by an invented horsepower-per-pound constant. Here horsepower is force times speed over 33,000, the definition of the unit, so pull, speed, duty and efficiency each move the result.

Which duty service factor should I use?

Use 1.5 for continuous running with gradual loading. Frequent starts, full-load starting or indexing take 2.0, and severe duty 2.5 to 3.0, per the drive guide's duty bands.

Why divide by drive efficiency?

The gearbox and belt drive consume part of the motor's output before it reaches the belt. Dividing by the measured or quoted efficiency sizes the motor for the power the belt actually receives.

Why is the minimum rating blank above 200 HP?

The screening list covers standard NEMA sizes only. A larger drive needs an engineered selection with acceleration torque, thermal rating and the manufacturer's frame data, which this page does not attempt.

Conveyors calculator

Conveyor Motor HP Calculator

Size a conveyor drive from its belt pull and belt speed with the standard horsepower relation. Enter the duty service factor and drive efficiency to get the design motor HP and the next standard NEMA size.

What this calculator does

Design motor horsepower from belt pull and speed after the duty factor and drive efficiency, with the next standard NEMA size.

Formula used

Belt pull × belt speed ÷ 33,000 gives screening horsepower; one horsepower is 33,000 foot-pounds per minute
Design motor horsepower = screening horsepower × duty service factor ÷ (drive efficiency ÷ 100)
Service factor added = design motor horsepower − screening horsepower
Minimum motor rating = design horsepower rounded up to the next standard NEMA size; blank above 200 HP

Inputs explained

Belt Pull (Effective Tension): Effective tension the drive must exert, from a pull calculation.
Belt Speed: Belt speed at the drive pulley, measured or from the gear ratio.
Duty Service Factor: Duty multiplier: 1.5 normal, 2.0 heavy, 2.5 to 3.0 severe.
Drive Efficiency: Motor and gearbox efficiency; 90% is a typical helical drive.

How to use the result

Best suited to screening a new conveyor motor size, checking a quoted motor against the duty, rechecking after a belt speed increase.
A screening model for standard NEMA sizes: above 200 HP the drive needs an engineered selection. Steady state only; it does not check acceleration torque, thermal duty or holding brakes.

Current U.S. benchmarks

The U.S. has 21,668 machinery manufacturing establishments employing about 1,086,146 workers (Census County Business Patterns, 2023).

Common questions

How is this different from the old factor? The old page multiplied a load in pounds by an invented horsepower-per-pound constant. Here horsepower is force times speed over 33,000, the definition of the unit, so pull, speed, duty and efficiency each move the result.
Which duty service factor should I use? Use 1.5 for continuous running with gradual loading. Frequent starts, full-load starting or indexing take 2.0, and severe duty 2.5 to 3.0, per the drive guide's duty bands.
Why divide by drive efficiency? The gearbox and belt drive consume part of the motor's output before it reaches the belt. Dividing by the measured or quoted efficiency sizes the motor for the power the belt actually receives.
Why is the minimum rating blank above 200 HP? The screening list covers standard NEMA sizes only. A larger drive needs an engineered selection with acceleration torque, thermal rating and the manufacturer's frame data, which this page does not attempt.

Last reviewed 2026-10-01.