Wire Size Calculator
Calculate the correct electrical wire gauge for your project based on current, voltage drop, and distance
Electrical Wire Size Calculator
Choose your electrical system type
System operating voltage
Typically 3-5% for most applications
Wire conductor material
Maximum expected current (peak load)
Distance from source to load (one-way)
Maximum expected operating temperature
Recommended Wire Size
Cross-sectional Area
AWG Wire Gauge
Calculation Method: A = I × ρ × 2L / V
Adjusted Resistivity: 2.05e-8 Ω⋅m at 75.0°C
System: Single-phase DC/AC
Wire Size Analysis
Example Calculation - 120V Single-Phase
Given Parameters
System: AC Single-phase
Voltage: 120V
Current: 25A
Distance: 100m (one-way)
Voltage Drop: 3% (3.6V)
Material: Copper at 50°C
Calculation Steps
Step 1: Adjust resistivity for temperature
ρ₅₀°C = 1.68×10⁻⁸ × [1 + 0.00404×(50-20)] = 1.88×10⁻⁸ Ω⋅m
Step 2: Calculate cross-sectional area
A = I × ρ × 2L / V = 25 × 1.88×10⁻⁸ × (2×100) / 3.6
Result: A = 26.1 mm² ≈ 3 AWG
Voltage Drop Guidelines
Common Applications
Residential: House wiring, outlets, lighting
Commercial: Building power distribution
DC Systems: Solar, battery, automotive
Motors: Pumps, HVAC, industrial equipment
Understanding Wire Size Calculations
Wire Size Formula
Wire size is calculated using Ohm's Law and Pouillet's Law to determine the minimum cross-sectional area needed to carry current within acceptable voltage drop limits.
Single-Phase Formula
A = I × ρ × 2L / V
Three-Phase Formula
A = 3 × I × ρ × L / V
- A: Cross-sectional area (m²)
- I: Current (A)
- ρ: Resistivity (Ω⋅m)
- L: One-way distance (m)
- V: Voltage drop (V)
Temperature Effects
Wire resistance increases with temperature, affecting the required wire size. The calculator adjusts for operating temperature using the temperature coefficient.
Temperature Correction
ρ₂ = ρ₁[1 + α(T₂ - T₁)]
- ρ₂: Resistivity at target temperature
- ρ₁: Resistivity at reference temperature (20°C)
- α: Temperature coefficient
- T₂ - T₁: Temperature difference
Safety Note: Always consult local electrical codes and a qualified electrician
AWG Conversion and Circular Mils
AWG Calculation
AWG = -39 × log₉₂(d/0.005) + 36
American Wire Gauge (AWG) provides a standardized way to specify wire sizes, where smaller numbers indicate larger wires.
Circular Mils
cmil = (diameter in mils)²
Circular mils (cmil) are commonly used in the US electrical industry. One cmil equals the area of a circle with 1 mil (0.001 inch) diameter.