WireGaugeCalc Free calculator · NEC cited · works offline
Watts Law Calculator
watts law calculator is fast with WireGaugeCalc, since you enter any two of power, voltage, and current and the tool solves the third.
It uses the relationship P equals V times I, so you can check a load before you size the circuit.
The payoff is the watts, volts, or amps you need without rearranging the formula 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.
How The Power Formula Drives The Result
Power equals voltage times current, so knowing any two values lets the calculator solve the one you are missing.
Since the math is simple but easy to flip, the tool keeps the inputs separate so you read the right result for the load.
What The Watts Law Tool Solves
WireGaugeCalc handles the three values in the power formula:
- Power in watts from volts times amps
- Current in amps from watts divided by volts
- Voltage in volts from watts divided by amps
- Single value solve from any two inputs
- Quick check before sizing a circuit
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 is the difference between Watt's law and Ohm's law?
Watt's law links power, voltage, and current as P equals V times I, while Ohm's law links voltage, current, and resistance as V equals I times R. This tool solves the power side. Use either to cross check a load and confirm circuit limits against the current NEC and your local authority having jurisdiction.
How do I find amps from watts and volts?
Divide the watts by the volts to get the current in amps. Enter the watts and volts and the calculator returns the amps 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.