To find the amount of PFC your system needs, use a **power quality analyser** to directly measure a circuit’s power factor. You can also use the power factor correction calculation formula:

Qc = P (tan ϕ – tan ϕ')

- Qc is the total reactive power (kVAr)
- P is the Active Power (kW)
- ϕ is the initial phase shift angle
- ϕ' is the compensated phase shift angle

The phase shift angle is the timing difference between the system’s current and voltage. It is the horizontal offset in the plots in the PFC circuit example above, and it too can be measured with a **power quality analyser**.

Once you’ve determined the total reactive power, you’ll need to determine how to achieve that in capacitors: either individual ones next to their loads (ideal), or larger ones handling groups of loads, which may be necessary based on your system’s constraints.

If you don’t have the values for this power factor correction calculation, you’ll need to perform the detailed circuit calculations, which will vary with circuit complexity. For the above simple PFC circuit example, use the resistor’s Ohm value, the inductor’s Henry value, and the source’s Volt and Hertz values to determine the capacitor’s required Farad value.