Power Factor Equations

Power factor measures the phase angle between the instantaneous voltage and the instantaneous current in a circuit. Voltage leads current by 90° in an inductive circuit (ELI) and voltage lags current by 90° in a capacitive circuit (ICE).

A popular mnemonic is ELI the ICE man. (L for inductive and C for capacitive)


power factor ( Pf ) = cos ( q )Power factor equation formula - RF Cafe
Apparent Power ( P ) = I * V
True Power = P
I = Current
q = Phase angle
V = Voltage

Power Formulas
Apparent Power
P = I * V
P = I2 * R
P = V2 / R
True Power
P = I * V * cos (q)
P = I2 * Z * cos (q)
P = V2 * cos (q) / Z
P = Pa * Pf
Impedance
Z = V2 * cos (q) / P
Z = P / [I2 * cos (q)]
Current
I = P / [V * cos (q)]
I = sqrt {P / [Z * cos (q)]}
Voltage
V = P / [I * cos (q)]
V = sqrt [P * Z / cos (q)]
 

where

P = power in Watts
V = Voltage in Volts
I = current in Amps
R = resistance in Ohms (Ω)
Z = impedance in Ohms (Ω)
q = phase angle between I and V in degrees
Pa = apparent power in VoltˇAmps (VA)
Pf = power factor