Amp to Wire Size Calculator
Calculate the proper electrical wire size based on current requirements and system parameters
Electrical Wire Size Calculator
System current in amperes
Type of electrical system
System voltage in volts
Maximum allowable voltage drop (typically 3-5%)
One-way cable run distance
Wire conductor material
Maximum wire operating temperature
Wire Size Results
Recommended Wire Size
Formula used: A = φ × I × ρ × L / (V × %drop)
Phase factor (φ): 2.00 (single phase)
Resistivity at 50°C: 1.878 µΩ⋅cm
⚠️ Safety Notice
These results are for informational purposes only. Always consult a qualified electrician before proceeding with any electrical installation. Local electrical codes and safety requirements must be followed.
Example Calculation
Residential Circuit Example
System: 120V AC single-phase residential circuit
Current: 20 A (for a 20A breaker)
Distance: 30 meters (98 feet)
Voltage drop limit: 3%
Material: Copper wire
Calculation
A = φ × I × ρ × L / (V × %drop)
A = 2 × 20 × (1.68×10⁻⁸) × 30 / (120 × 0.03)
A = 2.016×10⁻⁵ / 3.6 = 5.6×10⁻⁶ m²
A = 5.6 mm²
Recommended: 10 AWG wire (5.26 mm²)
Common AWG Wire Sizes
Voltage Drop Guidelines
Residential: ≤ 3%
For branch circuits
Commercial: ≤ 5%
For feeder circuits
Motor circuits: ≤ 5%
Starting current consideration
Conductor Materials
Copper
• Most common conductor
• Excellent conductivity
• Corrosion resistant
Aluminum
• Lighter weight
• Lower cost
• Requires larger size
Understanding Wire Sizing
Why Wire Size Matters
Proper wire sizing ensures safe operation, prevents overheating, minimizes voltage drop, and meets electrical code requirements. Undersized wires can cause fires, while oversized wires increase costs unnecessarily.
Key Factors
- •Current carrying capacity (ampacity)
- •Voltage drop limitations
- •Operating temperature
- •Installation conditions
The Formula
A = φ × I × ρ × L / (V × %drop)
- A: Cross-sectional area (mm²)
- φ: Phase factor (2 for single-phase, √3 for three-phase)
- I: Current (amperes)
- ρ: Resistivity (Ω⋅m)
- L: Length (meters)
- V: Voltage (volts)
- %drop: Voltage drop percentage
Applications
Residential
Home wiring, appliance circuits, lighting systems
Commercial
Office buildings, retail spaces, industrial equipment
Automotive
Vehicle wiring, marine applications, RV systems