WireGaugeCalc Free calculator · NEC cited · works offline
NEC Service Load Calculation
NEC service load calculation is simple with WireGaugeCalc, since you enter the square footage and the connected loads and the tool totals them.
It applies the standard demand factors so the general lighting, appliances, and largest motor combine into one service size.
You get the calculated load and the matching service amps, so you can size conductors and the panel.
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.
How the NEC Load Calculation Adds Up
An NEC load calculation starts with 3 VA per square foot for general lighting, so the floor area drives the base load.
Demand factors then reduce the total, since not every circuit runs at full load at once.
The calculator adds fixed appliances, heating or cooling, and 25% of the largest motor to reach the final demand.
Inputs the Service Load Calculation Uses
The tool builds the demand load from the values you provide:
- Dwelling square footage
- Small appliance and laundry circuits
- Fixed appliance nameplate loads
- Range or cooktop demand
- Larger of heating versus air conditioning
- Largest motor at 125%
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
Do I use the larger of heating or cooling in the load calculation?
Yes, since both rarely run at the same time, the NEC lets you count only the larger of the two. The calculator drops the smaller value automatically.
Why is 25% of the largest motor added?
The NEC requires 125% of the largest motor load, so the extra 25% covers continuous running current. Always confirm the final demand against the current NEC and your local authority having jurisdiction before sizing the service.
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.