Choosing the wrong inverter size is the most common mistake we see. Too small, and it shuts down or overheats the moment a fridge or drill starts. Too big, and you pay for power you never use. This free calculator helps you pick the right size in under a minute.
Select the appliances you plan to run together, adjust the watts if needed and press the button. You will get the running load, the estimated start-up peak, the inverter size we recommend, and the battery voltage and waveform that suit it.
Inverter size calculator
Tick every appliance you want to run at the same time. Change the watts if your device is different.
| Appliance | Running watts | Qty | Surge |
|---|
Add your own device
How the inverter size calculator works
The calculator adds up the running watts of everything you tick, multiplied by the quantity. This is the continuous load your inverter has to supply. It then looks for the biggest start-up surge among your devices. Motors, compressors and pumps can briefly need two to three times their running watts when they switch on. Resistive devices like kettles and heaters need no extra surge.
Your recommended size is the larger of two numbers: the running load plus a 25 percent safety margin, or half of the peak load (because most inverters can surge to roughly twice their continuous rating for a moment). We then round up to the next common inverter size. Running an inverter close to its limit makes it hot and shortens its life, so the margin matters.
Tips for choosing the right inverter
Do not run everything at once
If you will use the microwave and the coffee maker at different times, tick only one of them. Sizing for devices that never run together makes the inverter bigger and more expensive than you need.
Avoid heating appliances on small inverters
Space heaters, kettles, toasters and hair dryers use 1000W to 1800W continuously. They drain a battery very quickly, so they are a poor match for most battery-powered setups.
Match the battery to the inverter
A bigger inverter needs a bigger battery and thicker cables. For loads above about 1000W, a 24V or 48V system is easier and safer than 12V. Our battery runtime calculator and cable and fuse calculator help with the next steps.
Frequently asked questions
What size inverter do I need for a refrigerator?
A full-size refrigerator usually runs at 100W to 250W but needs two to three times that to start. A 1000W pure sine wave inverter is often enough for a fridge alone, and 1500W gives more room.
Can I run a microwave on an inverter?
Yes, but a microwave rated at 1000W cooking power draws about 1400W to 1800W from the inverter. Plan for a 2000W inverter and a strong battery bank.
Should I choose pure sine wave or modified sine wave?
Pure sine wave is the safer choice for laptops, TVs, fridges and anything with a motor. Modified sine wave works for simple devices but can cause noise and heat.
How accurate is the result?
It is a good planning estimate. Always check the label on your own devices, because actual watts and surge vary by model.
Please note: These results are estimates for planning. For any inverter connected to house wiring, ask a qualified electrician to check the installation.