Wire Size Calculator
Find the minimum AWG wire gauge that meets both your voltage-drop limit and standard ampacity ratings.
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Wire Size Calculator
Results
- Minimum wire size
- 8 AWG
- Ampacity at this size
- 50 A
- Voltage drop at this size
- 2.51 V (2.09%)
- Voltage at the load
- 117.49 V
Guidance only — not a substitute for the NEC or local electrical code. Derating for conduit fill, ambient temperature, and terminations is not applied; consult a licensed electrician for actual installations.
About Wire Size Calculator
Enter the load current, run length, voltage, and allowed percentage drop, and the calculator walks the AWG table from 14 up to 4/0 to find the smallest conductor that satisfies both the drop limit and the ampacity rating for your chosen insulation temperature (standard 60/75/90°C columns).
The ampacity table is editable, so you can substitute derated values for hot ambients, bundled cables, or your local code's numbers.
Common uses
- Size the feeder for a subpanel, well pump, or EV charger run
- Pick wire for low-voltage solar and battery runs where drop dominates
- Compare copper vs aluminum for a long run
Limitations
- Guidance only — not a substitute for the NEC or local electrical code. Termination ratings, conduit fill, and ambient derating are not applied automatically; consult a licensed electrician for real installations.
Frequently asked questions
What does ampacity mean?
Ampacity is the maximum continuous current a conductor can safely carry without its insulation overheating. It depends on the insulation's temperature rating, which is why the calculator offers the standard 60, 75, and 90°C columns.
What size wire do I need for a 30 amp circuit?
On a short run, 10 AWG copper covers 30 A at the common 75°C termination rating (35 A ampacity). Over a long run the voltage-drop limit often forces a larger conductor, which is exactly the case this calculator checks for you.
Why does the calculator pick a bigger wire than the ampacity table suggests?
It enforces two constraints at once: the wire must carry the current safely and keep voltage drop under your limit. On long runs the drop limit usually dominates, so the answer lands one or more sizes above the bare ampacity minimum.
Is my electrical project data uploaded anywhere?
No. All sizing math, including any ampacity values you edit in the table, happens in your browser — nothing is sent to a server or retained.
Can I use this calculator instead of the electrical code?
No. It gives guidance from standard tables but does not apply derating for conduit fill, ambient temperature, or termination ratings. The NEC or your local code governs real installations, so have a licensed electrician verify the final size.