Power in AC circuits is much complicated than DC circuits.

• Real power: power loss due to heating through an ohmic material. It is also called resistive power loss. It is calculated by $I^2_{RMS}R$. Note that the phase needs to be considered. For example, if $I_{RMS}=(0.107 A \angle -63.4^\circ)$ and $R=50 \Omega$ (always 0 phase for resistor), the real power is: $-0.343W - j0.459W$, or $0.573 \angle -126.8^\circ$.
• Reactive power: power due to capacitance and inductance within a circuit. The reactive power is given in volt-ampere reactive, or VAR. $VAR=I^2_{RMS}X$. For example, in the same circuit is there is an inductor with 265mH, assuming AC is 60Hz, then the reactance $X_L=j \omega L= j(2 \pi * 60Hz*265 * 10^{-3}H)=j100\Omega = 100 \Omega \angle 90^\circ$. In this case $VAR=0.917VA-j0.686VA$, or $1.145VA \angle 36.8 ^\circ$.
• Apparent power: the total power flowing in an AC circuit. It is sum of reactive and real power: $VA=VAR+P_R$.
• Power factor is the ratio of consumed power to apparent power: $PF = \frac{P_{consumed}}{P_{apparent}}=\frac{P_R}{VA}$. It also means cosine theta of the phase angle between voltage and current. Power factor of a pure resistive circuit is 1, a pure reactive circuit is 0.