What Size Wire for 40 Amps at 50 Feet?

Answer
8 AWG copper

At 50 ft one way on a 240 V circuit, 8 AWG copper keeps voltage drop at 1.27%, under the recommended 3%. Ampacity alone would allow 8 AWG, but voltage drop decides the size at this distance. In aluminum, use 8 AWG.

Free, no sign-upInstant resultsUpdated October 2026
A
%
3% branch, 5% total (NEC note)
Phase
Conductor
Recommended wire
–
How we calculated this

    For estimating and educational purposes only. Results are approximate and are not a substitute for a licensed professional, the manufacturer's instructions or your local code. Disclaimer

    More questions like this

    15 amps20 amps30 amps30 A · 50 ft30 A · 100 ft30 A · 150 ft30 A · 200 ft40 amps40 A · 100 ft40 A · 150 ft40 A · 200 ft50 amps50 A · 50 ft50 A · 100 ft50 A · 150 ft50 A · 200 ft60 amps60 A · 50 ft60 A · 100 ft60 A · 150 ft60 A · 200 ft70 amps100 amps100 A · 50 ftAll quick answers

    Voltage drop by wire size (40 A, 50 ft, 240 V)

    Copper wireDrop (V)Drop (%)Within 3%
    8 AWG3.06 V1.27%✓
    6 AWG1.96 V0.82%✓
    4 AWG1.23 V0.51%✓
    3 AWG0.98 V0.41%✓
    2 AWG0.78 V0.32%✓

    Voltage drop = 2 × 50 ft × 40 A × resistance ÷ 1000. Keeping it under 3% on branch circuits (5% total) is the NEC recommendation in the informational notes to 210.19 and 215.2.

    Frequently asked questions

    Is 8 AWG enough for 40 amps at 50 feet?

    It carries 40 A, but at 50 ft the voltage drop is 1.3%, which is acceptable.

    Does the distance include the return wire?

    No. Enter the one-way distance; the formula already counts both conductors.

    Open the full calculator: Wire Size Calculator →