What Size Inverter Do I Need? Campervan AC Power Calculator
Campervan Inverter Size Calculator: Run AC Appliances Off-Grid
Sizing an AC inverter for your campervan is where most DIY electrical builds go wrong. If you want to run a 1000W microwave, buying a 1000W inverter seems logical—until you turn it on and the massive “startup surge” instantly trips the system. Furthermore, converting 12V battery power into household AC power requires massive amounts of DC current. If your cables and fuses are even slightly undersized, they will overheat and become a severe fire hazard.
Our interactive campervan inverter size calculator removes the dangerous guesswork. Select the appliances you plan to run simultaneously, and our engine will automatically calculate your total continuous load, your peak surge watts, and the exact heavy-duty wire gauge and inline fuses you need to keep your van safe.
⚡ AC Inverter Calculator
Size your inverter, cables, and fuses to prevent electrical fires.
Turn on the appliances you plan to run at the exact same time. (e.g. Will you run the AC while making coffee?)
Never max out an inverter continuously. We have automatically added a 20% safety buffer to your continuous watts to ensure the inverter’s cooling fans can keep the unit from overheating during extended use.
People Also Asked: Inverter Sizing & Safety
What is the difference between "Running Watts" and "Surge Watts"?
Running watts are the amount of power an appliance uses continuously to stay on. Surge watts (or Peak watts) are the massive, split-second spike of electricity required to jumpstart a motor or a compressor. For example, a rooftop air conditioner might only use 1200W to run, but it can demand up to 2500W for a fraction of a second just to start up. If your inverter isn't rated to handle that surge, it will shut down and scream at you with a red fault light.
Pure Sine Wave vs Modified Sine Wave: Which is better?
You must buy a Pure Sine Wave inverter. "Modified Sine Wave" inverters are cheaper because they produce a choppy, blocky electrical signal. While they can run simple tools or old incandescent lightbulbs, they will cause laptops to glitch, coffee makers to run dangerously hot, and eventually permanently destroy sensitive electronics like CPAP machines and Starlink routers.
Does leaving my inverter turned on drain my battery?
Yes. Inverters are constantly searching for a load, and keeping the internal components energized creates "standby draw." A large 2000W or 3000W inverter can drain roughly 1 to 2 Amps per hour just sitting idle. Over a 24-hour period, a forgotten inverter can drain 48Ah from your system—which is nearly half the usable capacity of a standard 100Ah battery!
💡 Van Life Hack: Wire your inverter to a remote switch mounted in your living area. Get in the habit of keeping the inverter turned OFF unless you are actively plugging something into an AC wall socket.
Why do I need such thick cables for my inverter?
Because you are pulling household power from a 12V battery. To make 2000 Watts of AC power, the inverter has to suck a massive amount of DC current out of your batteries (often over 170 Amps). If you use thin wires, that electrical friction turns into extreme heat. Never cut corners here: always use pure copper (not CCA) 1/0 AWG or thicker cables for 2000W+ inverters.
Where is the safest place to mount an AC Inverter?
You need to keep the DC cables between your battery and the inverter as short as physically possible (under 3 to 5 feet) to prevent voltage drop and overheating. However, do not mount the inverter in the same unvented sealed box as Lead-Acid or AGM batteries, as a tiny spark from the inverter could ignite the hydrogen gas they produce. (This is another reason why sealed Lithium batteries are far superior).
Can I run an air conditioner off solar power and an inverter?
Yes, but it is incredibly expensive. Running a 1200W air conditioner through an inverter will completely drain a massive 300Ah Lithium battery bank in roughly 3 hours. To run an AC unit off-grid, you need a minimum of 600Ah of Lithium batteries, a 3000W inverter, and a roof completely covered in solar panels (at least 800W) just to slow down the drain.