Wire Size Calculator
Find the correct AWG wire gauge for your electrical project. Enter your circuit parameters and get NEC-compliant wire sizing with voltage drop analysis.
How to Use the Wire Size Calculator
Find the right wire gauge in three simple steps.
Enter Circuit Parameters
Input the load current in amps, one-way wire length, system voltage, conductor material (copper or aluminum), and phase type.
Click Calculate
Press Calculate to instantly get the recommended AWG wire size based on ampacity and voltage drop calculations.
Review NEC Compliance
Check the recommended AWG size, actual voltage drop in volts and percentage, and whether it passes the NEC 3% standard.
AWG Ampacity Reference Table
NEC 75°C column ampacity ratings for copper and aluminum conductors.
| AWG Size | Copper (A) | Aluminum (A) | Resistance (Ω/1000ft Cu) |
|---|---|---|---|
| 14 AWG | 15 | — | 2.525 |
| 12 AWG | 20 | 15 | 1.588 |
| 10 AWG | 30 | 25 | 0.998 |
| 8 AWG | 50 | 40 | 0.628 |
| 6 AWG | 65 | 50 | 0.395 |
| 4 AWG | 85 | 65 | 0.248 |
| 2 AWG | 115 | 90 | 0.156 |
| 1 AWG | 130 | 100 | 0.124 |
| 1/0 AWG | 150 | 120 | 0.098 |
Frequently Asked Questions
Common questions about wire sizing and AWG.
For 20 amps at 120V with copper wire, you typically need 12 AWG wire for runs up to about 50 feet. Longer runs may require 10 AWG to keep voltage drop below 3%.
Longer wire runs increase resistance and voltage drop. To maintain voltage drop below 3%, longer runs require larger gauge wire. A 100-foot run at 15A may need 10 AWG while a 25-foot run can use 14 AWG.
The NEC recommends that voltage drop on branch circuits should not exceed 3% at the farthest outlet, and total voltage drop including feeders should not exceed 5%. This ensures equipment operates efficiently and safely.
Copper has lower resistance and higher ampacity than aluminum of the same gauge. Copper is preferred for branch circuits. Aluminum is lighter and cheaper but requires larger gauges for the same current capacity.
Undersized wire causes excessive voltage drop, overheating, wasted energy, and is a fire hazard. It can damage sensitive electronics and cause motors to run inefficiently or fail.