Wire Size Calculator

Wire Size Calculator sizes a conductor for a real circuit, in both directions - and shows the NEC table figures behind the answer.

Use this wire size calculator to find the conductor size a circuit needs, or check the voltage drop for a size you already have in mind, using NEC conductor tables. Every table value applied to your circuit is shown on screen so you can check the math.

WIRE SIZE
- Enter load current, one-way run length, system voltage, phase, conductor material, and a maximum voltage drop percentage
- Get a recommended conductor size, with the ampacity-required size and voltage-drop-required size shown side by side
- See which constraint governs, and a plain-language sentence explaining why
- View the full derating breakdown: base table ampacity, ambient temperature correction factor, conductor-count adjustment factor, and the resulting allowed ampacity
- Set termination temperature rating, ambient temperature, and number of current-carrying conductors
- Save a circuit; the first saved circuit needs no ad

VOLT DROP
- Pick a conductor size and see the resulting voltage drop in volts and as a percent of system voltage, using the same circuit inputs as the Wire Size tab
- A meter shows where the drop falls against the 3% branch-circuit and 5% total advisory figures
- See the next larger standard size and the drop it would produce
- Log a result to a running history list; logging needs no ad, and the saved history list unlocks with a short rewarded ad

CIRCUITS
- Save the current circuit's inputs and its recommended size
- Reopen a saved circuit to reload its figures
- Delete any saved circuit
- The first saved circuit needs no ad; saving more unlocks with a short rewarded ad

WHAT IT CALCULATES
This app implements NEC conductor ampacity tables, ambient temperature correction, conductor-count adjustment, and a standard resistance-based voltage-drop formula. It is a calculation aid, not a substitute for a licensed electrical design - the authority having jurisdiction and the code edition actually adopted for an installation govern. Always verify against the locally adopted code and, where required, a licensed electrician or engineer.

BUILT FOR THE JOB SITE
- Fast entry with minimal taps
- Works offline on site or in the panel room
- No account required
- Your saved circuits and history stay on your device

This app is ad-supported. Sizing and voltage-drop calculations are always available; saving beyond the first circuit or viewing your logged history unlocks with a short rewarded ad.

Recent changes:
First release.

Enter a circuit and the app returns the conductor size the NEC tables call for, or the voltage drop for a size you pick.

Every table figure it applied is shown on the result.