# Why does my Kill-a-Watt read Power of only half the Voltage times Current?

My Kill-a-Watt is displaying that its output is 120 V, 0.16 A, and 10 W.

I'm confused... I thought P = V × I from basic EE. Why do I see only half the expected value here?

(This is a USB charger, and I'm trying to calculate the charger output current indirectly.)

• Your math is confused. Vrms * Irms = 120V * 0.16A = 20VA. And 10 != 2 * 20. (Which is lucky, because a power factor of 2.0 is impossible) May 16 '16 at 5:04
• @BenVoigt: Fixed the typo May 16 '16 at 5:20

• The portion of your answer concerning phase is correct, but runs into the problem in the presentation of your question where you claim that the power factor is 2.0 -- There's no phase leading to a power factor > 1.0, because power factor is cos(Vphase-Iphase) May 16 '16 at 5:08