WireGaugeCalc Free calculator · NEC cited · works offline
20 Amp 250 Feet
20 amp 250 feet is simple with WireGaugeCalc, since you enter 20 amps, the voltage, and the 250 foot run and the tool returns a conductor size.
The calculator checks the NEC 310.16 ampacity for your material, then it measures voltage drop across the full distance.
You get a gauge that holds the load and keeps the drop under control over a long run.
Open the calculatorEnter any two values and read the rest.
Ohm’s law: V = I × R and P = V × I. Field aid only, verify against the current NEC and your local authority having jurisdiction.
Why 250 Feet Often Upsizes The Conductor
A 20 amp load needs only 12 AWG copper for ampacity at the 60 degree C column, so distance is what drives the gauge here.
Resistance grows with length, so voltage drop builds over 250 feet.
WireGaugeCalc upsizes the conductor until the drop stays inside the 3% branch-circuit guideline.
What The 250 Foot Result Covers
The calculator weighs both ampacity and run length:
- NEC 310.16 ampacity for the chosen material
- 12 AWG copper as the ampacity baseline for 20 amps
- Voltage drop checked against the 3% target
- One-way run length of 250 feet entered directly
- Copper or aluminum conductor selection
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 12 AWG enough for 20 amps at 250 feet?
12 AWG copper carries 20 amps for ampacity, but over 250 feet the voltage drop can pass 3 percent. The calculator may suggest 10 AWG or larger to keep the drop in check.
What voltage drop target should I aim for?
The NEC recommends about 3 percent on a branch circuit and 5 percent total feeder plus branch as a guideline. Confirm conductor size and any derating 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.