WireGaugeCalc Free calculator · NEC cited · works offline
Find The Voltage Drop From C T Od
Find the voltage drop from c t od is fast with WireGaugeCalc, since you enter the gauge, length, and current.
The calculator returns the volts lost on the run and the percent drop for the circuit.
So you can hold the line within the 3% branch-circuit guideline before the wire is pulled.
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.
Calculate Volts Lost On The Run
Voltage drop grows with run length and current, so a long feeder loses more than a short branch circuit.
WireGaugeCalc uses the conductor resistance, the one-way distance, and the load to return the drop in volts and percent.
Since copper has lower resistance than aluminum, the tool adjusts the result for the metal you select.
Keep The Drop Within The Guideline
The calculator finds the voltage drop using these inputs:
- Wire gauge and conductor material
- One-way run length of the circuit
- Load current in amps
- System voltage and single or three phase
- Percent drop against the 3% 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 suggests holding branch-circuit drop near 3 percent and the combined feeder plus branch near 5 percent. These are recommendations in informational notes, not strict code limits.
How do I lower a voltage drop that is too high?
Increase the wire gauge or shorten the run, since both cut the resistance the current sees. Verify the final conductor size against the current NEC and your local authority having jurisdiction.
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.