What Size Power Inverter do I Need?

Power inverters are a great tool to have on your vehicle rather it be a car, truck, motorhome, or even a boat. They are able to provide you with a source of alternating current (AC) power so that you are able to run common household items such as laptops, coffee makers, televisions, or whatever else is needed. In most cases they will have to be installed by hooking directly to your vehicle’s battery and then routing the inverter cables through your car’s firewall. Smaller sized models though can typically plug right into your vehicle’s built-in dash charger.

One of the most common questions we get on power inverters is what size of inverter should you purchase? Now inverters come in four main sizes. The lowest, or smallest, is between two-hundred to four-hundred watts. These are the units that can plug into your car’s dashboard without any real setup. The downside here is that four-hundred watt limit typically does not have enough capacity to power larger or more complex appliances. The other common sizes of inverters are one-thousand watts, two-thousand watts, and three-thousand watts. There are some four-thousand watt and larger models out there, but these are rarely needed.

When it comes to choosing a power inverter’s size bigger is not always better. The larger the unit the more power that is going to route through it which means the more power you will need either from your vehicle’s alternator or battery. With these really large units you will most likely need to either have a high capacity alternator installed or an alternative deep cycle battery installed. In some cases it is recommended to have both installed so that your vehicle can handle the large power loads required for a three or four-thousand watt inverter.

Determining the correct size power inverter for your needs is actually quite easy. All you need to do is add up all of the wattage requirements of the appliances you wish to power. For example, if appliance A has a wattage of four-hundred and appliance B has a wattage of three-hundred then it would make sense to purchase a one-thousand watt inverter. If you find that you are unable to find the wattage requirements on an appliance then you can also look at the appliance’s amperage draw. This is typically labeled as ‘5 Amps,’ or something similar.

Once you know the amperage you can find the watts very easily. Just take the amperage amount times the volt. Volts are determined by the type of plug-in the appliance has. If it plugs into the standard outlet found throughout your home then it requires one-hundred and twenty volts. The math would be amperage times volts. An example would be a coffee machine that requires six amps. Six amps times one-hundred and twenty volts equals seven-hundred and twenty watts required.

When you have the total wattage needs calculated it is also safest to add an additional twenty to thirty percent to that number. Using the same example from above with the coffee machine we have a wattage amount of seven-hundred and twenty required. If we add thirty percent we get an amount of just over one-thousand. There is your number. To run your coffee machine along with a twenty/thirty percent addition you would need a one-thousand watt inverter.


Simply repeat this process for however many appliances you wish to power with your vehicle. Remember though folks that you need to be aware that the power routing through your inverter comes from your vehicle. If you are not careful or if you do not install an alternative deep cycle battery then you could end up with a dead battery due to the power draw. Not will the battery need jump started but it could also shorten the life span of that battery.

For more on this topic I recommend checking out our power inverter’s buying guide which can be found by clicking here.

Thanks for reading,

Alec Johnson

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