The torque requirement for an application can be calculated, measured directly using a torque measuring device (torque watch), or measured indirectly using a DC motor. When using a motor, measure the current draw of the motor under load, and calculate the torque using the equation below:
          T = (I - INL) x (KT x N x h)

Where

I = Current
T = Torque
KT = Torque Constant
N = Gear Ratio (Equals 1 if there is no gearbox) h = Gearbox Efficiency (Equals 1 if there is no gearbox)
INL = No-Load Current

     Please be aware that this equation approximates the true load torque and does not take thermal conditions into consideration. The results are reasonably close and suitable for most purposes.

HORSEPOWER OF A MOTOR

     A motor’s Hp (Horse Power) is calculated using the following equation.
          Hp= (T (lb-ft) x N (rpm)/5252. This gives the Hp at a rated speed.

     The output speed for a motor or gearmotor is given by the equation below:
          w = [VS - (I x Rmt)] / (KE x N)

Where