The Following conveyor belt capacity charts show tons per hour (TPH) based on material weighing 100 lbs. per cubic foot, 20° material surcharge angle with three equal length rolls on troughing idlers. CAPACITY (TPH) =.03 x Belt Speed (FPM) x material weight (lb. per cu. ft.) x load cross section (sq. ft.) TPH with 20° Troughing Idlers