WireGaugeCalc Free calculator · NEC cited · works offline
Ac Voltage Drop Calculator
ac voltage drop calculator is quick with WireGaugeCalc, since you enter the conductor size, run length, and load and the tool returns the volts lost.
You pick copper or aluminum, and the calculator shows the drop against the 3 percent branch circuit guideline.
The payoff is a clear voltage figure so you can find voltage drop before the run is too long.
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 Run Length And Material Let You Find Voltage Drop
Voltage drop rises with distance and load, so a longer run loses more volts at the same conductor size.
Copper carries with less resistance than aluminum, so the material you choose changes the drop the calculator reports.
What The Potential Drop Calculator Reads
WireGaugeCalc checks the inputs that set the drop on an AC run:
- Conductor size in AWG or kcmil
- One way run length
- Load current in amps
- Copper or aluminum material
- Percent drop against the 3 percent branch circuit guideline
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 voltage drop is acceptable on a branch circuit?
The NEC has an informational guideline of 3 percent on a branch circuit and 5 percent total across feeder and branch. It is a recommendation, not a hard rule, so confirm your target against the current NEC and your local authority having jurisdiction.
Does copper or aluminum give more voltage drop?
Aluminum has higher resistance per size than copper, so the same run in aluminum shows more drop. The potential drop calculator switches the value when you change the material.
How do I lower voltage drop on a long run?
Increase the conductor size or shorten the run, since both reduce the volts lost. Use the calculator to find voltage drop again after bumping the wire up a size.
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.