Power factor measures the phase angle between the instantaneous voltage and the instantaneous current in a circuit.
Voltage (E) leads current (I) by 90° in an inductive (L) circuit
and voltage (E) lags current (I) by 90° in a capacitive (C) circuit.
A popular mnemonic is ELI the ICE man since E is leading (coming before) I in
ELI, and E is lagging (coming after) I in ICE.
power factor ( P_{f} ) = cos ( q ) 

Apparent Power ( P ) = I * V 
True Power = P 
I = Current 
q = Phase angle 
V = Voltage 
Power Formulas 
Apparent Power P = I * V P = I^{2}
* R P = V^{2} / R 
True Power P = I * V * cos (q) P
= I^{2} * Z * cos (q) P = V^{2} * cos (q) / Z P = P_{a} * P_{f} 
Impedance Z = V^{2} * cos (q)
/ P Z = P / [I^{2} * 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 P_{a}
= apparent power in Volt·Amps (VA) P_{f} = power factor 

