WireGaugeCalc Free calculator · NEC cited · works offline
20 Amp Gauge Wire Length
20 amp gauge wire length is fast with WireGaugeCalc, since you enter the breaker rating, conductor material, and run distance and it returns the gauge that fits.
The calculator starts from 12 AWG for a 20 amp circuit per NEC 310.16, then checks whether your run length forces a larger size to hold voltage drop under 3%.
So you confirm the right wire before you pull cable, not after.
Open the calculatorSmallest conductor whose ampacity meets the load, NEC Table 310.16. Field aid only, verify against the current NEC and your local authority having jurisdiction.
Why run length changes the wire size on a 20 amp circuit
A 20 amp breaker normally protects 12 AWG copper at a 75 degree termination, so that is the starting point the calculator uses.
As the run gets longer the voltage at the load drops, so the calculator may step you to 10 AWG to keep drop within the 3% guideline.
It shows both the ampacity-based size and the length-driven size so you can pick the larger one.
What WireGaugeCalc checks for a 20 amp run
Enter a few values and the tool sizes the conductor for both heat and distance:
- Breaker rating set to 20 amps as the load reference
- Copper or aluminum, since aluminum carries less current per size
- One-way run length in feet to estimate voltage drop
- 12 AWG copper baseline from NEC 310.16
- An upsize to 10 AWG when a long run pushes drop past 3%
- Termination temperature column used for the rating
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
How far can I run 12 AWG on a 20 amp circuit?
12 AWG copper at full 20 amp load reaches roughly 50 feet before voltage drop nears 3 percent. Beyond that the calculator usually suggests 10 AWG. Verify the result against the current NEC and your local authority having jurisdiction.
Does a lighter load let me run 12 AWG farther?
Yes, since voltage drop depends on the actual current, not just the breaker. Lower the load amps in the calculator and the allowable length grows.
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.