WireGaugeCalc Free calculator · NEC cited · works offline
Calculate Voltage Drop
calculate voltage drop quickly with WireGaugeCalc, since the app uses the conductor resistance, run length, and load current to return the loss as a percent.
You enter the voltage, the one-way distance, the amps, and whether the wire is copper or aluminum, then the app does the math.
You see whether the run stays under the 3 percent guideline, so you can upsize the wire before the run is in the wall.
Open the calculatorUses Vd = (phase factor × K × I × L) / circular mils, K = 12.9 copper, 21.2 aluminum. Field aid only, verify against the current NEC and your local authority having jurisdiction.
How the voltage loss calculator handles long runs
Voltage drops over distance because every foot of conductor adds resistance, so a long run loses more than a short one at the same current.
Aluminum has higher resistance than copper, so the app adjusts the loss when you switch the conductor material.
When the result climbs past 3 percent, you bump up the wire size and the percent falls back into range.
What you need to compute voltage drop
Enter the inputs that drive the result:
- System voltage, such as 120, 240, or 480
- One-way run length in feet
- Continuous load current in amps
- Conductor material, copper or aluminum
- Conductor size in AWG or kcmil
- Single-phase or three-phase wiring
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
Is the 3 percent voltage drop limit a code requirement?
The 3 percent figure for branch circuits is a recommendation in the NEC, not a hard rule, while feeders and branch circuits together are suggested to stay near 5 percent. Confirm the target against the current NEC and your local authority having jurisdiction.
Why does copper beat aluminum on the same run?
Copper has lower resistance per foot than aluminum, so it drops less voltage at the same gauge and current. To match copper performance, aluminum usually needs to go up a size or two.
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.