Wire Size Calculator
Determine the correct wire gauge to minimize voltage drop and ensure safety.
Standard: 3% for critical, 5% for non-critical.
How to Calculate Wire Size
Selecting the correct wire size is critical for electrical safety and efficiency. An undersized wire can overheat (fire hazard) or cause significant voltage drop (equipment failure).
This calculator considers two primary factors: Ampacity and Voltage Drop.
1. Ampacity (Current Carrying Capacity)
Ampacity is the maximum current an insulated conductor can safely carry without exceeding its insulation temperature rating.
- Copper vs. Aluminum: Copper is a better conductor and can carry more current than an aluminum wire of the same size.
- Temperature Rating: This tool uses the standard 75°C column from NEC Table 310.16, which is a safe baseline for most modern terminations.
2. Voltage Drop
Even if a wire can handle the heat (ampacity), long distances introduce resistance that lowers the voltage at the load end.
Recommended Limits (NEC 210.19):
- 3% Max Drop: For sensitive electronics, lighting, and branch circuits.
- 5% Max Drop: For general appliances and feeder circuits.
Calculation Formula
The voltage drop is calculated using the formula:
Vdrop = (K × I × L) / A
Where:
- K: Specific resistivity (12.9 for Copper, 21.2 for Aluminum).
- I: Current in Amps.
- L: Length of the wire (2x for DC/1-Phase).
- A: Cross-sectional area in Circular Mils (cmil).
Common Wire Sizes & Applications
| AWG Size | Typical Ampacity | Common Use |
|---|---|---|
| 14 AWG | 15 Amps | Lighting circuits, standard outlets |
| 12 AWG | 20 Amps | Kitchen/Bathroom outlets, AC units |
| 10 AWG | 30 Amps | Electric dryers, water heaters |
| 8 AWG | 40-50 Amps | Electric ranges, large ACs |