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 

