Wire Size Calculator
Determine the minimum wire gauge (AWG) for your electrical circuit based on amperage, distance, voltage, and allowable voltage drop. References NEC ampacity tables for copper and aluminum conductors.
Results
Recommended Wire Size
10 AWG
Copper
Actual Voltage Drop
6.01V
2.50%
Conduit Size (min.)
1/2"
EMT
Wire Ampacity (75°C)
35A
NEC 310.16
Min. by Ampacity Only
10 AWG
NEC table
Min. by Voltage Drop Only
10 AWG
3% max
How to Use This Calculator
Enter the circuit amperage, one-way wire distance in feet, system voltage, phase type, conductor material, and your maximum acceptable voltage drop percentage. The calculator selects the smallest wire size that satisfies both NEC ampacity requirements and your voltage drop limit.
Formula Used
Voltage Drop = (K x I x D) / cmil. Where K = 2 x resistivity (single phase) or 1.732 x resistivity (three phase). Copper resistivity = 10.4 ohm-cmil/ft. Aluminum = 17.0 ohm-cmil/ft. Wire must also meet NEC Table 310.16 ampacity at 75C.
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Disclaimer
This calculator is for estimation purposes only. Results may vary based on local conditions, materials, and building codes. Always consult a licensed professional before making decisions based on these calculations. MyContractorTools is not responsible for any errors or omissions.