WireGaugeCalc Free calculator · NEC cited · works offline
Electric Vehicle Charging Calculator
Electric vehicle charging calculator from WireGaugeCalc is quick to use, since you enter the charger amperage and voltage and it sizes the circuit.
The calculator treats EV charging as a continuous load, so it adds the 125 percent factor the NEC requires before picking the breaker and conductor.
You see the breaker and wire size in seconds, so an EVSE circuit is planned without working each rule by hand.
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.
Sizing an EVSE Circuit
EV chargers run for hours at a time, so the calculator sizes the circuit to 125 percent of the charging current.
It reads conductor ampacity from NEC 310.16, so the wire matches the breaker after the continuous load factor is applied.
The tool ties every result to the termination temperature, so the rating you read matches the lugs on the charger and breaker.
What the Charging Calculator Checks
The calculator works through the EVSE sizing steps in order:
- Applies the 125 percent continuous load factor
- Picks a breaker rated for the adjusted current
- Sizes the conductor to meet the breaker rating
- Compares copper and aluminum at the same load
- Holds to the termination temperature column
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 an EV charger circuit use 125 percent?
EV charging is a continuous load that runs three hours or more, so the NEC requires the circuit to be sized at 125 percent of the charging current. Confirm the factor and the charger rating against the current NEC and your local authority having jurisdiction.
What breaker does a 40 amp charger need?
A 40 amp charger draws a continuous 40 amps, so it needs a 50 amp breaker after the 125 percent factor. The calculator applies this automatically when you enter the charger amperage.
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.