Enter any two of power, energy, and time (with unit choices for each) to solve for the third.
How to Use the Wattage Calculator
Solve for power, energy, or time using the toggle at the top. Energy accepts joules, watt-hours, or kilowatt-hours; time accepts seconds, minutes, or hours — pick whichever unit matches the number already in hand and the calculator handles the conversion internally.
Power, in the everyday sense of "how many watts is this drawing," is a rate: energy consumed divided by the time it took to consume it. That's a different question from the V × I calculation the Power Calculator on this site handles — this one starts from a usage total, not from voltage and current readings.
P = E ÷ tA device that uses 2 kWh over 2 hours is averaging exactly 1,000 W across that window — 1 kW, in other words, whether it actually drew a flat 1,000 W the whole time or spiked and dipped around that average. That distinction matters: this calculator returns an average, not an instantaneous reading, which is the right number for budgeting energy costs but the wrong one for checking whether a device will trip a breaker at its peak draw.
The unit dropdowns exist because energy shows up in wildly different scales depending on context — a phone battery's rating in Wh, a utility bill in kWh, a physics problem in joules — and converting by hand before typing a number in is one more place to introduce an error. For a single appliance's running cost rather than its average wattage, the Electricity Calculator on this site is the more direct tool.