Inverter Calculator | What Size Inverter Do You Need In Your Campervan Conversion?

Graham Bogie

This inverter calculator will help you correctly size your inverter for the daily load of your AC appliances in your camper.

It’s simple and straightforward to use. However, we’ve included a section below to answer some questions you may have.

This calculator forms part of our camper solar setup series and the broader subject of campervan electrics

And it’s just one of our electrical calculators for RVs and campervan conversions.

Calculating the inverter size, and understanding the implications, may help you assess the appliances you need in your RV and look for DC alternatives or more efficient devices.

Get this right for your camper lifestyle, and you can confidently complete your DIY campervan conversion.

Check out our detailed post on campervan power inverters to see how they work and how to install them.

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How do I use this inverter calculator?

  1. Enter every electrical AC device and component you’ll use in your camper
  2. Enter the watts each device uses
  3. That’s it.

Do I need an inverter?

No! If you only use DC appliances, you don’t need an inverter.

You only need an inverter to use AC appliances powered by your deep cycle battery.

If you use AC appliances when hooked up and the battery powers them, you still need an inverter.

You don’t need an inverter if you use AC appliances only when hooked up and with AC sockets on the mains circuit.

Consider installing a combined RV inverter charger if you also need a converter (to convert AC power to DC).

Can I avoid needing an inverter altogether?


We have an article about inverters for RVs, which explains how to avoid the need for an inverter altogether.

How do I know all the electrical devices I’ll use?

The most critical part of sizing the electrical system is to get a complete list of electrical appliances, devices, and components you’ll use in your RV.

Underestimate it, and you may run out of power.

Overestimate, and you’ll probably spend more money and make your setup more complex than necessary.

Work through your typical day, considering all the appliances you’ll use along the way. 

You’ll need a complete list of all AC and DC appliances to work out the total solar battery bank.

Mark up the AC components to calculate the inverter size needed.

I won’t use all my devices every day. What should I enter in the calculator?

The calculation aims to size the inverter so it can handle the AC devices you will run.

It’s important to understand that the inverter is sized to cope with load at any one time. 

Even if you only use your powerful hairdryer for a few minutes every couple of days, add it to the list so we can size an inverter to handle it.

How do I know if my appliance is AC or DC?

The labels or specifications of most appliances state whether it is AC or DC.

Failing that, if it has a plug you could use in your household sockets, it is probably an AC appliance.

How do I find the watts of each device?

The watts of most devices can be found either printed on the device, in the operating manual, or on the manufacturer’s website online.

Sometimes, products list the power usage in current (i.e. amps). In this case, use the wattage calculator above to convert the current and volts to watts.

I have more than 5 devices. What shall I do?

If you have more than 5 AC devices to list, follow these steps:

  1. Enter the 1st 5 devices
  2. Press the “add more devices” button
  3. A further 5 rows are displayed for you to add more devices and another “add more devices” button.

You can add up to 25 devices in total.

I have more than 25 devices. What shall I do?

Enter the 25 most powerful devices. 

Why is the minimum size inverter so small?

Inverters add load to the electrical system, even with no connected appliances. The larger the inverter, the greater that base load.

So it’s a complete waste to install an oversized inverter for your needs.

The smallest inverter you can get away with is one that can run the most powerful AC device on your list with no other load.

Why is the maximum size inverter so big?

You may want to use multiple AC devices at the same time.

If so, you’ll need an inverter to cope with the total load at any one time.

The maximum size inverter assumes all your devices will be used simultaneously. If this is not the case for your setup, only enter the devices you’ll use concurrently. 

Make sure to include the most powerful device if it’s bigger than the combined watts of the other appliances.

I don’t use all my appliances at the same time. What size inverter do I need?

If you only use one device at a time, you need the recommended minimum size inverter.

If you will use multiple devices at the same time, work out the highest total wattage of the combined appliances and use those to calculate the inverter size needed.

I want a much bigger inverter than the calculator has worked out. What shall I do?

We’ve included a mini calculator above that shows how much battery and solar power you need to run your appliances for a single hour.

The solar array shown would need 4 good hours of sun to replace the battery energy used by the inverter.

Adjust the solar panels accordingly if you expect more or less peak sun hours.

Simply enter the size of the inverter you want.

There is a health warning on my results. What does it mean?

Inverters and AC appliances are inherently power hungry and can quickly drain batteries.

A 1000w inverter fully loaded for an hour will drain around 84 amps from the battery. 

To replace that 84 amps, you’ll need a 1000w solar array with 4 good hours of sun.  

Remember, you can only take out of the battery what you put in.

I received a message that all my devices are too powerful. What should I do?

The biggest size inverter you can realistically run in an RV or camper is about 3000 watts.

If your smallest AC device needs an inverter larger than 3000w, consider a less powerful appliance, a DC alternative, or running it on an AC mains circuit when hooked up.

I received a message that I couldn’t run all my devices simultaneously. What should I do?

You may not intend to run all your appliances at the same time, in which case you can ignore this message.

But if you do, consider less powerful appliances, DC alternatives, or running them on an AC mains circuit when hooked up.

The estimated battery bank size and solar array are massive. Is this correct?

Yes! It’s surprising, isn’t it?

Maybe give some thought to cutting back on your electrical needs.

The estimated battery bank size and solar array are much bigger than I have space for. What should I do?

Now is definitely the time to reconsider your electrical needs and how you can meet them.

Need more help calculating your campervan electrical components?

Here are the links to our other calculators:

In Conclusion

The most important thing to remember when choosing an inverter for your campervan is to get one that is the right size for your needs.

An inverter that is too small will not be able to run all of your devices, and one that is too large will be a waste of space and money. Use the inverter calculator above to help you determine the perfect size for your campervan conversion.

What size inverter do you use in your campervan? Leave a comment and let us know!

Graham Bogie

Graham Bogie - Expert in RV & Campervan Electrics - Mowgli Adventures

Graham is a seasoned marine electrical engineer with two decades of experience designing customized electrical systems for plant machinery and converting campers and overland vehicles. His expertise has led him to author the reputable Campervan Electrics Handbook and become the chief designer of our Campervan Electrical Design Service. As a knowledgeable figure in the field, his YouTube channel, blog, Facebook group, and newsletter, offering electrical advice and product reviews, reach more than a million users each year.

2 thoughts on “Inverter Calculator | What Size Inverter Do You Need In Your Campervan Conversion?”

  1. hello i am Mr Paul Stevens, i have a pellet heater, 12 Kw with a 400 watt max use, i wish to protect it from power outage, and would like to use a 12 Volt with a charger permanent in charging , this heater is to run 24 hours per day, can you please advise me of the correct inverter to use, thank you in advance.

    • Hi Paul
      The pellet heater needs at least a 500w inverter. Are you intending to run this off your AC, only using the inverter when there’s a power outage or are you just running the 12v fan from the battery permanently? If the former, you’ll need an inverter/charger. So long as the inverter side of the combo unit is greater than 500w (and they pretty much all are), you’ll be good.


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