WireGaugeCalc Free calculator · NEC cited · works offline
No Outage Voltage Drop Calculator
no outage voltage drop calculator is quick with WireGaugeCalc, since you enter the run length and load and it returns the percent drop.
It measures the drop against the 3 percent branch-circuit guideline, so you see if a long run starves the load.
The payoff is a sized conductor that holds voltage without tripping or browning out equipment.
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 Load Set The Drop
Voltage drop climbs with distance, so a longer one-way run pushes the percent higher.
Copper and aluminum behave differently, since aluminum has more resistance per foot.
The 3 percent guideline marks the branch-circuit target, as larger drops cut usable voltage at the device.
Inputs For The Voltage Drop Check
A few values produce the percent drop:
- One-way run length in feet
- Load in amperes on the circuit
- System voltage, such as 120 or 240
- Conductor material, copper or aluminum
- Compares the result to the 3 percent guideline
- Suggests upsizing when the run runs long
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 hard rule?
It is a recommendation in the NEC informational notes, not an enforced limit, but most shops treat 3 percent on a branch circuit as the working target. Confirm any required value against the current NEC and your local authority having jurisdiction.
Should I use one-way or round-trip length?
Enter the one-way distance, since the calculation already accounts for current flowing out and back. Doubling it yourself would overstate the drop.
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.