WireGaugeCalc Free calculator · NEC cited · works offline
Home Generator Wattage Calculator
home generator wattage calculator is simple with WireGaugeCalc, since you list each appliance and the tool totals the running watts.
It also adds the surge watts that motors draw at startup, so the generator can handle the moment a compressor or pump kicks on.
You get a total wattage target, so you can size a generator that carries the whole load without stalling.
Open the calculatorEnter any two values and read the rest.
Ohm’s law: V = I × R and P = V × I. Field aid only, verify against the current NEC and your local authority having jurisdiction.
Running Watts Plus Starting Watts
The calculator sums the steady running watts of every load you select, so you see the continuous demand.
It then adds the largest starting surge, since a motor can pull several times its running watts for a second when it spins up.
That combined number tells you the minimum generator size to keep lights and appliances on.
What the Wattage Total Includes
The result blends a few load factors:
- Running watts for each appliance you add
- Starting watts for the largest motor load
- Refrigerator, sump pump, and furnace fan surges
- Lighting and small plug-in loads
- A margin so the generator is not run at full output
One app for every NEC calculation
WireGaugeCalc keeps the calculations you reach for most in one place:
- Voltage drop and wire sizing for any run
- Conduit fill for EMT, PVC, and RMC
- Box fill and junction box sizing
- Ampacity and temperature derating
- Motor circuit and load calculations
- Conduit bend offsets and saddles
Built for the field, works offline
The whole app runs on your phone, so it keeps working in a basement, an attic, or a job site with no signal.
There is no account to create and nothing to load. Open it, run the number, and get back to work.
- No signup and no signal needed
- Answers in a tap, not a spreadsheet
- Same tool on phone, tablet, and desktop
Every result cites the NEC article
Each answer shows the table or formula it came from, so you can check the method and learn the code as you go.
That makes the app useful on the job and during exam prep, since the reasoning is right next to the number.
Switch the code year your job runs on
Jurisdictions adopt the NEC at different times, so you can match the calculation to the code in force:
- NEC 2017, 2020, and 2023 tables
- Copper and aluminum conductors
- 60, 75, and 90 degree C terminations
- Single-phase and three-phase systems
Run the number, then get back to work
Stop flipping through a paper book or hopping between calculator sites. Enter your values, read the code-cited answer, and move on. Free to use, no signup.
Open the calculatorFrequently asked questions
Why does the starting watts number matter so much?
Motors in pumps, compressors, and HVAC draw a brief surge well above their running watts, so the generator must supply that peak or it can stall. Sizing only to running watts often leaves you short when a motor starts.
Should I add a margin above the total?
Yes, leaving headroom keeps the generator from running at full output for long stretches. Confirm the transfer equipment and wiring against the current NEC and your local authority having jurisdiction before connecting to the home.
Is WireGaugeCalc free to use?
Yes. Every calculator is free to run with no signup. A paid tier adds saved projects, PDF reports, and extra code years, but the core math stays free.
Does it work without internet?
Yes. The app runs on your device, so it keeps working with no signal on a job site, in a basement, or in an attic.
Are the results code accurate?
Results follow published NEC tables and standard formulas, and each answer shows the article it came from. It is a field aid, not a stamp of approval, so verify against the current code and your local authority before you wire anything.
Which NEC code year does it use?
You can switch between NEC 2017, 2020, and 2023, since jurisdictions adopt the code at different times. Pick the year your job runs on.