Wire Size Calculator
Calculate Wire Size
Calculate the correct wire gauge for electrical circuits based on current load, voltage drop, and ambient temperature. This calculator ensures safe and code-compliant electrical installations.
How Wire Size Calculator Works
Proper wire sizing is critical for electrical safety and efficiency. The calculator considers current-carrying capacity, voltage drop limitations, and temperature derating to recommend the appropriate wire gauge.
Key Sizing Factors
- Current Load: The actual amperage the circuit will carry
- Safety Factor: NEC requires 125% of continuous load capacity
- Voltage Drop: Must not exceed 3% for branch circuits (5% total)
- Temperature Derating: Higher temperatures reduce current capacity
- Conduit Fill: Multiple wires in conduit require derating
Current Carrying Capacity (Ampacity)
| Wire Size | Copper (A) | Aluminum (A) | Common Use |
|---|---|---|---|
| 14 AWG | 15 | - | Lighting circuits |
| 12 AWG | 20 | 15 | General outlets |
| 10 AWG | 30 | 25 | Electric dryers, A/C |
| 8 AWG | 40 | 30 | Electric ranges |
| 6 AWG | 55 | 40 | Large appliances |
Temperature Derating
Correction Factors for 90°C Insulation:
- 21-25°C: 1.08 (can carry more current)
- 26-30°C: 1.00 (rated capacity)
- 31-35°C: 0.91
- 36-40°C: 0.82
- 41-45°C: 0.71
Voltage Drop Guidelines
- Branch Circuits: Maximum 3% voltage drop
- Feeder + Branch: Maximum 5% total voltage drop
- Motor Circuits: Often limited to 3% for proper starting
- Sensitive Equipment: May require even lower voltage drop
Wire Material Considerations
Copper Wire
- • Higher conductivity
- • Better corrosion resistance
- • Easier to work with
- • Higher cost
- • Preferred for most applications
Aluminum Wire
- • Lower cost
- • Lighter weight
- • Requires special terminations
- • Larger size needed for same current
- • Used for feeders and service entrance
Safety Considerations
- Always follow local electrical codes and regulations
- Consider future load growth when sizing conductors
- Use proper overcurrent protection for wire size
- Account for parallel runs in large installations
- Verify termination temperature ratings
- Consider environmental factors (moisture, chemicals)
Cite this page as:
Daniel, P. Wire Size Calculator. Available at: https://constructioncalculators.com/wire-size-calculator/. Accessed: October 25, 2026.