Generator Wattage Calculator
Add up appliance running and surge watts from an editable checklist to get a recommended generator size.
Processed locally in your browser — nothing is uploaded.
Generator Wattage Calculator
| Use | Appliance | Running W | Surge W | Remove |
|---|---|---|---|---|
Results
- Total running watts
- 800 W
- Largest single surge premium
- 1,500 W
- Required capacity
- 2,300 W
- Recommended generator size
- 2,760 W
Motors draw far more at start-up; only one is assumed to start at a time.
Required capacity plus 20% headroom.
Default wattages are typical values — check each appliance's nameplate. Running a generator near its maximum continuously shortens its life; oversizing slightly is safer than undersizing.
About Generator Wattage Calculator
Tick the appliances you need to run at once — each row has editable running and surge watts with typical defaults. The recommendation adds all running watts plus the single largest surge premium (motors briefly draw several times their running power at start-up), then 20% headroom.
Common uses
- Size a portable generator for storm outages (fridge, sump pump, lights)
- Plan a job-site or camping generator around specific tools
- See how much adding a window AC changes the requirement
Example
Input
Fridge 700/2200 W + sump pump 800/2000 W + lights 100 W
Output
1,600 W running · 3,100 W required · ≈ 3,720 W recommended
Limitations
- Defaults are typical values — use each appliance's nameplate. Assumes only one motor starts at a time.
Frequently asked questions
What is the difference between running watts and surge watts?
Running watts is what an appliance draws continuously; surge (starting) watts is the brief spike a motor pulls at start-up, often two to three times its running draw. A typical refrigerator runs at about 700 W but surges to around 2200 W.
What size generator do I need to run a refrigerator?
A generator that can deliver the fridge's surge — roughly 2200 W for a typical unit that runs at 700 W. Check the compressor's nameplate, since starting watts vary considerably between models.
Why does the calculator only add one surge value?
Motors rarely start at the exact same instant, so the standard sizing method adds all running watts plus only the single largest surge premium above running. If two big motors genuinely can start together, add the second surge yourself.
Is my appliance list stored online anywhere?
No. The checklist and any wattages you edit live only in your browser for the current visit — nothing is uploaded or saved to a server.
How much headroom should a generator have?
The recommendation adds 20% above the calculated requirement. Running a generator near its limit invites tripped overloads when a surge lands, and continuous full-load operation is harder on the engine.