Van life · power
Van inverter size calculator.
Add the AC appliances that run at the same time to find the continuous watts, the surge, and the large DC current your battery cable and fuse must handle.
Inputs
Inverter needed
Enter your numbers.
How to size an inverter for a van
Add the running watts of everything that runs at the same time. Peak demand is that total plus the largest single start-up surge above its running watts, because motors and compressors do not all start together. Add headroom, then check the battery current: DC amps = running watts / (battery volts x inverter efficiency).
Worked example. All five default loads together run at 1,175 W. The biggest surge is the blender (800 W start, 400 W run, so 400 W extra), so peak is 1,575 W. With 25% headroom the suggested continuous rating is 1,469 W. At 12 V and 90% efficiency the battery supplies 109 A at the running load and 146 A at peak.
Safety. Currents of this size need heavy cable, short runs and a fuse or breaker rated for the inverter, sized from the inverter manual, not from this page. Use the voltage drop tool to check cable length. The starting-watt figures here are placeholders; read the real ones off your appliance labels or manuals.
Frequently asked questions
What size inverter do I need for a van?
Add the running watts of loads that run together, add the largest start-up surge, then add headroom. With the example loads that is 1,175 W running and 1,575 W at peak.
How many amps does a 1000W inverter draw from a 12V battery?
About 1000 / (12 x 0.9) = 93 A at 90% efficiency, which is why the cable and fuse must be heavy.
What is the difference between running and starting watts?
Running watts are what an appliance draws steadily. Starting watts are the brief higher draw at start-up, common in compressors and motors.
Should I use a 12V, 24V or 48V system?
Higher voltage cuts the current for the same watts, so cables can be lighter. This tool shows the amps for each choice so you can compare.
Sources
Checked
Runs entirely in your browser. Nothing you type is sent or stored.
Planning estimate, not professional advice
Results are planning estimates from the numbers you enter. They are not professional, engineering, electrical or safety advice and are not a substitute for the manufacturer's instructions or local code. Battery banks, inverters and DC wiring can start fires or injure you if built wrongly: size cable and fuses to the equipment manual, fuse every positive conductor close to the battery, and have a qualified electrician check the build.