  # Power Factor Equations

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 ( Pf ) = 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 = 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 WattsV = Voltage in VoltsI = current in AmpsR = resistance in Ohms (Ω)Z = impedance in Ohms (Ω)q = phase angle between I and V in degreesPa = apparent power in Volt·Amps (VA)Pf = power factor    About RF Cafe Copyright: 1996 - 2024Webmaster:    Kirt Blattenberger,    BSEE - KB3UON RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling 2 MB. Its primary purpose was to provide me with ready access to commonly needed formulas and reference material while performing my work as an RF system and circuit design engineer. The Internet was still largely an unknown entity at the time and not much was available in the form of WYSIWYG ... All trademarks, copyrights, patents, and other rights of ownership to images and text used on the RF Cafe website are hereby acknowledged. My Hobby Website:  AirplanesAndRockets.com 