Single phase Motor Capacitor Calculation calculator

Single-phase motor Capacitor calculator:

Enter the input voltage, motor power in watts, efficiency in percentage, frequency, then press the calculate button, you get the required capacitance value.

Enter Motor Power In Watts: W
Enter Motor Efficieny: %
Enter input Voltage: V
Enter Frequency: Hz
Result – Required Capcitance : µF

Single-phase motor Capacitor Calculation Formula:

Initially single phase motor needs little rotor push to rotate the rotor at the rated RPM. Selection of right capacitor for single-phase motor is really tough, it could lead to starting the motor or not.

The single-phase capacitance C(µF) in microfarad is equal to 1000 times the product of power P(W) in watts and efficiency η divided by the product of voltage V(V) in volts square and the frequency F(Hz).  The formula for calculating capacitor value is

C(µF) = (P(W) x η x 1000) / (V(V) x V(V) x f)

Look at the formula, the required capacitance value is directly proportional to the motor power. Hence while increasing the motor size, the size of capacitance also will be increased.

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The calculation for Voltage Rating of the Capacitor:

The voltage rating of the capacitor is equal to the product of the voltage measured at both ends of the main winding in volts and the root of one plus turns ratio n square.

V(C) = Vp √(1+n2)

n is equal to the ratio between the main/auxiliary winding turns. The above formula is used to find the approximate voltage across the capacitor.


Calculate the rated required capacitance value for the single-phase, 220V, 1 HP, 50Hz, 80% of the motor.

1 HP = 746 Watts.

Use our capacitance calculation formula.

C(µF) = 746 x 80 x 1000 / (220 x 220 x 50) = 24.66 µF.

Hence 1 HP Motor required 24.66 µF capacitance to start the motor smoothly. But in the market, you can get 25 µF.

The voltage range for the capacitor should be 440V min.


In the same way, let us take another example:

Calculate starting capacitance for single phase 70 Watts, 220 V, 50 Hz, 85% efficiency fan.

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C(µF) = 70 x 80 x 1000 / (230 x 230 x 50) = 2.459 µF. approx. 2.5 µF.

Hence you can cross verify our calculation with your fan.

The voltage range for the capacitor should be 440V min.


  1. Hi Sir, the calculating formula, is this for a start-capacitor, or for a run-capacitor.
    If you like it to send me an answer,Thanks in advance.


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