WireGaugeCalc Free calculator · NEC cited · works offline
Find Max Motor Amperage
Find max motor amperage is fast with WireGaugeCalc, which returns the motor full-load current you need from horsepower, voltage, and phase.
Enter the nameplate values and the calculator pulls the full-load amps so you can size conductors and protection.
You get the current figure right away, so you can move on to wire and breaker sizing without hand math.
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.
Motor Full-Load Current Without the Guesswork
The tool uses the standard NEC motor full-load current values, since the code sizes conductors from those tables rather than nameplate amps.
You enter horsepower, voltage, and single or three phase, so the result matches how electricians size a motor branch circuit.
Conductors for a single motor are sized at 125 percent of the full-load current, so the calculator gives you the base number to multiply.
What the Motor Amperage Result Covers
The result is built around the figures that drive a motor branch circuit:
- Full-load current from horsepower and voltage
- Single-phase and three-phase options
- The 125 percent conductor multiplier for a single motor
- Copper and aluminum conductor ampacity for the run
- Common 120V, 208V, 240V, and 480V supply values
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
Should I size conductors from the nameplate amps or the NEC table?
Use the NEC full-load current tables to size conductors and overload protection for the motor branch circuit. The nameplate amps are used for the overload device setting. Verify the values against the current NEC and your local authority having jurisdiction.
Why is the conductor sized at 125 percent of full-load current?
A single continuous-duty motor needs conductors rated at least 125 percent of the full-load current, since the motor draws sustained current and starts under load. The calculator shows the base current so you can apply the multiplier.
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.