Volts to watts calculator

What is a volts to watts calculator?

A volts to watts calculator converts an electrical voltage and current into electrical power. Power, measured in watts (W), tells you how much energy a device uses or produces each second. Because most appliances list their voltage and current draw, this tool makes it easy to find the wattage you need when sizing a power supply, an inverter, a generator, or a circuit breaker.

Formula

Electrical power is the product of voltage and current:

where $P$ is power in watts, $V$ is voltage in volts, and $I$ is current in amperes. This relationship holds directly for direct current (DC) circuits and for resistive alternating current (AC) loads where voltage and current are in phase.

How to use

1. Enter the voltage of the device in volts (V).
2. Enter the current it draws in amperes (A).
3. Read the resulting power in watts (W). The result appears automatically once both fields are filled in.

Worked example

Suppose a device runs at 120 volts and draws 5 amps of current:

So the device consumes 600 watts of power.

FAQ

Does this formula work for AC circuits?

It works exactly for DC circuits and for purely resistive AC loads. For reactive AC loads (motors, transformers), the true power is $P = V \cdot I \cdot \text{pf}$, where pf is the power factor between 0 and 1, so the actual watts will be lower than volts times amps.

How do I go back from watts to amps?

Rearrange the formula to $I = P / V$. Divide the power in watts by the voltage in volts to get the current in amps.