Watts, amps and volts converter
Many appliance labels list amps, not watts. Convert them here before you add them to a generator plan.
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Amps → watts
Watts → amps
Answers
8 A at 120 V
960 W
1,500 W at 120 V
12.5 A
Formula: watts = volts × amps × power factor. Amps = watts ÷ (volts × power factor).
The one formula you need
For household sizing, watts = volts × amps. A tool labeled 8 amps at 120 volts uses about 960 watts. A 240-volt well pump labeled 9.8 amps uses about 2,350 watts. Virginia Cooperative Extension’s appliance energy guide recommends exactly this when a nameplate lists amps but not watts: multiply the current by the voltage the appliance uses, 120 V for most plug-in items and 240 V for large appliances such as dryers, ranges, and many well pumps.
What power factor means (and when to ignore it)
For heaters, incandescent bulbs, toasters, and other resistive loads, the voltage and current rise and fall together, so the formula is exact. Motors and some electronics draw current slightly out of step with voltage. The result is that the “real” watts are a little lower than volts × amps; the ratio is called the power factor. If a nameplate lists it, enter it. If not, leaving it at 1.0 overestimates slightly, which is the safe direction when sizing a generator.
Nameplate amps are a maximum
The amp figure on a label is usually the maximum draw, not the average. A refrigerator labeled 6 amps rarely draws 720 watts continuously; the compressor cycles. For sizing a generator, the maximum is what matters, because the generator must handle it when it happens. For estimating fuel or energy use, the average is more useful.
12-volt conversions
The 12 V setting is for DC gear in RVs, boats, and vehicles. A 12-volt fridge drawing 5 amps uses about 60 watts. Remember that an inverter converting battery power to 120 V AC loses some energy, so the battery supplies a bit more than the appliance uses.
Next step: add the watts to the generator size calculator, or check an RV hookup with the RV amp calculator.