WireGaugeCalc Free calculator · NEC cited · works offline
Southwire Voltage Drop
southwire voltage drop checks are fast with WireGaugeCalc, since you enter the load, the run length, and the conductor and the tool returns the percent drop.
The calculator compares the result against the 3 percent branch-circuit guideline, so you can tell at a glance whether the gauge holds the voltage.
You get the same kind of answer in your browser, so you size the run without leaving the job.
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.
What a southwire voltage drop calculator measures
Voltage drop rises with current and distance, so a long run at high amps loses more voltage along the conductor.
A southwire voltage drop calculator divides the lost voltage by the supply voltage, so it reports the drop as a percentage you can judge.
WireGaugeCalc flags a run that clears 3 percent, so you can upsize the conductor before the device starves.
Inputs that drive the voltage drop result
The percentage moves with a handful of values:
- Source voltage and phase
- Load current in amps
- One-way run length in feet
- Conductor size in AWG or kcmil
- Copper versus aluminum resistance
- Power factor on inductive loads
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 limit should I aim for?
The common target is 3 percent on a branch circuit and about 5 percent total from the service to the load. These figures are NEC recommendations rather than hard limits, so confirm any requirement with the current NEC and your local authority having jurisdiction.
Why does copper beat aluminum on the same run?
Copper has lower resistance per foot, so for the same gauge it drops less voltage over the run. To match copper with aluminum you usually upsize the aluminum conductor a step 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.