Generator Wattage Calculator
Free generator wattage calculator. Tick the appliances you want to run to get the running and starting watts and the recommended generator size in watts and kilowatts.
About This Free Online Generator Wattage Calculator
Our free generator wattage calculator tells you what size generator to buy. Tick the appliances you want to power — fridge, microwave, AC, lights, furnace, well pump and more — set the quantity of each, and add any custom loads. The tool adds up the running watts, finds the starting (surge) watts of motor-driven appliances, and recommends a generator size with 15% headroom, shown in watts and kilowatts. Everything runs in your browser — perfect for backup power, camping and job-site planning.
Features of Our Generator Wattage Calculator
- Running watts from a checklist of common appliances
- Starting (surge) watts for motor-driven loads
- Custom running and starting loads for anything not listed
- Recommended generator size with 15% headroom, in W and kW
- Adjustable quantity per appliance
- 100% client-side and private — instant results, no signup
How to Use the Generator Wattage Calculator
Using this tool is simple and requires no signup or registration. Follow these steps:
- Tick each appliance you want to run and set its quantity.
- Add any custom running and starting watts not on the list.
- Review the running load and starting surge.
- Read off the recommended generator size in watts and kilowatts.
Frequently Asked Questions About Generator Wattage Calculator
How do I size a generator?
Add up the running watts of everything you want to power, then add the highest single starting (surge) watt of any motor — like a fridge, AC or well pump — on top. Add 15 to 20% headroom for safety. The calculator does this and recommends a generator size.
What is the difference between running and starting watts?
Running (rated) watts are what an appliance draws steadily. Starting (surge) watts are the brief extra draw when a motor starts — often 2 to 3 times the running watts. Generators are rated by both, and you need enough to cover the largest surge.
What size generator runs a refrigerator?
A typical fridge needs about 200 running watts but up to 1,200 starting watts. So a 2,000 watt generator easily handles a fridge plus lights and small electronics. Tick the fridge and a few items in the calculator to confirm.
Can this calculator handle a whole-house generator?
Yes. Tick every major appliance you want to back up — AC, furnace, well pump, fridge, lights — and the calculator adds the running watts and largest surge to recommend a whole-house generator size in kilowatts.
Is this generator calculator free?
Yes, completely free with no signup. All estimates run in your browser — nothing is uploaded or tracked.
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