How this calculator works
Power is the rate of electrical energy transfer. For steady DC, voltage multiplied by current gives watts. Single-phase AC uses RMS voltage and current multiplied by power factor to find average real power. For a purely resistive AC load the power factor is one. This page treats positive consumption; use the AC wattage page for balanced three-phase loads.
Formula
DC: P = VI. Single-phase AC: P = Vrms Irms PF. V = P/(I PF) and I = P/(V PF), with PF = 1 for DC.
Worked example
A 12 V DC supply delivering 2 A transfers 24 W. A 60 W DC load drawing 3 A operates at 20 V.
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Frequently asked questions
Are watts and watt-hours the same?
No. Watts measure power; watt-hours measure accumulated energy.
Can I use the current rating on a supply?
A rating is the maximum available current. Enter the actual load current to estimate actual power.
How do I handle three-phase power?
Use the related AC wattage calculator and choose the line-to-line or line-to-neutral voltage reference.