WireGaugeCalc Free calculator · NEC cited · works offline
Service Load Calculation
Service load calculation is simple with WireGaugeCalc, since you list the loads and the tool totals them into a service size.
The calculator applies the NEC Article 220 demand factors so the amperage reflects real-world diversity.
You get a defensible service size before you order 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 Dwelling Service Load Adds Up
A dwelling service uses demand factors because not every load runs at once, so the calculated amps sit below the raw connected total.
WireGaugeCalc applies the general lighting, appliance, and largest-motor rules from Article 220 to reach the demand load.
It converts the result to amps at the service voltage so you can pick 100, 150, or 200 amp.
What The Service Load Calculation Includes
The total comes from several pieces:
- General lighting load based on square footage
- Small-appliance and laundry branch circuits
- Fixed appliances like the range, dryer, and water heater
- Heating or air conditioning, taking the larger value
- The 25 percent add for the largest motor
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
What size service does a typical house need?
Many homes land at 150 or 200 amp once the demand factors are applied to the connected load. Run your loads through WireGaugeCalc and verify the result against the current NEC and your local authority having jurisdiction.
Why is the calculated load lower than the sum of all appliances?
Article 220 applies demand factors since loads rarely all draw at the same time, so the service can be smaller than the raw total. The calculator handles those factors for you.
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.