How do you figure out how big of a power inverter to use?

Determining Size of Power Inverter Needed

Generally power inverters are designated by how much power they are capable of putting out. Usually this is indicated in Watts, which is a universally accepted unit of power measurement.

For example, I have a 120 Volt / 1,000 Watt inverter which I use with my 12 Volt pickup truck battery. That one thousand watt specification indicates that it will operate a 120 Volt electrical device that uses 1,000 Watts [or less]. Commonly, to save line space, the Wattage is expressed in Kilowatt [Kw] units, with 1Kw meaning 1,000 Watts. Thus, you will see various designators such as 1.2 Kw [1,200 Watts], or 3Kw [3,000 Watts], etc.

To determine what size inverter you need, it is necessary to carefully examine the ID labels on the electrical devices that you want, or may want, to power from the inverter.

Usually these labels or decals will specify their voltage and wattage, BUT SOMETIMES they will not specify Wattage, instead giving an Amperage [Amps] rating. You can convert this Amperage draw info into Watts by multiplying the Volts [for example, 125 Volts] times the Amps [for example 10 Amps] to calculate the Watts [thus 1,250 Watts in this example].

Thus knowing the Wattage demand of your appliances or electrical devices, you can decide which ones, and their total wattage demand, and thus the size of the power inverter you need.

Remember that the inverter does not have to be large enough to operate all the devices at the same time, just the sum Wattage of the most heavy power users you would want to use at the same time.