A watt calculator finds electrical power in watts from voltage and current, or converts between watts, volts, amps and ohms. It’s useful for sizing extension cords, choosing a power supply, planning solar setups or estimating the energy cost of appliances.
The power formula is watts = volts × amps. A device drawing 2 amps at 120 volts uses 240 watts. Rearranged, amps = watts ÷ volts, so a 1,500-watt space heater on a 120-volt circuit draws 12.5 amps. Ohm’s law, volts = amps × ohms, connects resistance too, giving watts = amps² × ohms and watts = volts² ÷ ohms.
Energy cost: kilowatt-hours (kWh) = watts × hours ÷ 1,000. A 100-watt gaming PC running 5 hours a day uses 0.5 kWh daily, about 15 kWh a month. At 15 cents per kWh, that costs about $2.25 a month. A 1,500-watt heater running 6 hours a day uses 9 kWh daily, which adds up fast.
Safety tips: don’t exceed a circuit’s capacity; a standard 15-amp household circuit at 120 volts handles about 1,800 watts, and it’s best to stay below 80 percent of that for continuous loads. Use extension cords rated for the load, and consult a licensed electrician for wiring work.
Why use an online Watt Calculator: it saves time, avoids simple arithmetic mistakes and shows each step, so you can check your homework, plan a project or make a decision with confidence. Bookmark the page so it’s ready the next time you need it.
Tips for getting accurate results from the Watt Calculator: double-check that every input uses the right units, enter numbers without commas or symbols, and run the calculation a second time with a quick estimate in your head to confirm the answer looks reasonable.
Learn more on Wikipedia’s watt article. Find BTU, CFM and RPM calculators on Minedit.