Volts to Watts Calculator

How to use the volts to watts calculator

Enter the voltage and the current, and you get the power in watts — watts = volts × amps. This tool is framed for the case where you already know your system’s voltage: a 12 V car circuit, a battery bank, a 48 V solar string. You know the volts and you’ve measured the amps; you want the watts.

Why the voltage-known case deserves its own tool is that it starts from a different place than household AC work. Wiring a 120 V outlet, you usually begin with a device’s wattage and work out the amps. In DC and battery systems you usually begin with a known system voltage and a measured current, and want the wattage that represents — which is exactly this direction.

The math is watts = volts × amps, exact for DC and resistive loads. For AC motors the real power is a little less than volts × amps because their power factor is below 1, but the DC, battery, and resistive systems this tool targets follow it exactly. Enter the actual system voltage, not a household default.

It fits sizing a 12 V automotive accessory or its fuse, checking a solar string’s power (string voltage × string current), or budgeting a battery bank’s draw. A 48 V solar string at 8 A is 384 W; a 12 V winch pulling 40 A is 480 W; a 24 V trolling motor at 30 A is 720 W.

Volts and amps trade off for a given power. The same 1,200 W is 10 A at 120 V but only 5 A at 240 V — which is why solar strings, EV packs, and long DC runs use high voltage: less current means thinner wire and lower losses. If you know the watts and want the current instead, the amps-to-watts and watts-to-amps tools cover the other directions.

The formula

Power is voltage times current, exact for DC and resistive loads (AC motors draw slightly less real power — power factor):

watts = volts × amps

Worked example with the defaults — 120 V × 10 A = 1,200 W. A 12 V automotive circuit at 5 A is 60 W; a 48 V solar string at 8 A is 384 W.

For a fixed power, volts and amps trade off: 1,200 W is 10 A at 120 V but only 5 A at 240 V. Higher voltage means lower current for the same watts — the reason DC systems run high voltage to cut wire size and loss.

Frequently asked questions