Wire Gauge Calculator (AWG)
Calculate the recommended AWG wire gauge for your electrical circuit based on current, voltage, distance, and acceptable voltage drop. View ampacity ratings, resistance values, wire dimensions, and a complete AWG reference table — all calculated privately in your browser.
Calculate Wire Gauge
AWG Reference & Conversion
| AWG | Diameter (mm) | Diameter (in) | Area (mm²) | Area (kcmil) | Resistance (Ω/km) Cu | Resistance (Ω/1000ft) Cu | Ampacity (Cu, 60°C) |
|---|
AWG to mm² Conversion
How the Wire Gauge Calculator Works
This wire gauge calculator determines the correct American Wire Gauge (AWG) size for your electrical circuit by analyzing four key parameters: current draw in amps, supply voltage, one-way conductor distance, and your maximum acceptable voltage drop percentage. The calculator uses the resistivity of copper (1.724 × 10⁻⁸ ohm-meters) or aluminum (2.65 × 10⁻⁸ ohm-meters) to compute the minimum conductor cross-sectional area required. It then maps that area to the nearest standard AWG size that meets both the voltage drop and ampacity requirements. The tool supports single-phase and three-phase calculations, and distance inputs in both feet and meters.
Voltage Drop Formula
Vdrop = (2 × I × L × ρ) / A
Amin = (2 × I × L × ρ) / Vdrop(max)
Where: I = current (amps), L = one-way length (meters), ρ = resistivity (ohm-meters), A = cross-section area (m²). For three-phase, the factor 2 becomes √3.
The NEC (National Electrical Code) specifies that branch circuits should have no more than 3% voltage drop, and the total voltage drop from service entrance to the farthest outlet should not exceed 5%. This calculator defaults to 3% but lets you adjust this value for your specific application, whether you are wiring a residential circuit, running power to an outbuilding, or sizing conductors for industrial equipment.
Understanding AWG Wire Sizes
The American Wire Gauge system assigns a number to each standard wire size, where smaller numbers indicate thicker wires. AWG 0000 (4/0) is 11.684 mm in diameter, while AWG 40 is just 0.0799 mm — thinner than a human hair. Each step in AWG corresponds to a specific ratio: every 6 AWG steps doubles the wire diameter, and every 3 AWG steps doubles the cross-sectional area. Common residential wires include AWG 14 (15A circuits), AWG 12 (20A circuits), and AWG 10 (30A circuits). For long runs, heavy appliances, or sub-panels, you may need AWG 8, 6, 4, 2, or even larger conductors. The reference table below shows all standard gauges from 0000 to 40 with diameter, area, resistance, and ampacity ratings.
Voltage Drop and Wire Sizing Tips
Voltage drop increases with wire length and current, and decreases with larger conductor area. Long cable runs — such as powering a detached garage, barn, or workshop — require upsizing the wire gauge to keep voltage drop within acceptable limits. A 100-foot run carrying 20 amps on AWG 12 copper has roughly 3.2% voltage drop at 120V, which is borderline. Upgrading to AWG 10 cuts the drop to about 2% for the same run. Aluminum conductors have about 61% the conductivity of copper, so aluminum wire must be one or two sizes larger to match the performance of copper. Always verify your calculations against local electrical codes and consult a licensed electrician for safety-critical installations.
Copper vs Aluminum Conductors
Copper wire is the standard for most residential and commercial wiring due to its superior conductivity, flexibility, and corrosion resistance. Aluminum wire is significantly lighter and cheaper, making it the preferred choice for utility transmission lines and large feeder cables (AWG 4 and above). However, aluminum has higher resistance per unit length and expands more with heat, which requires special connectors and installation techniques. For service entrance cables and large branch circuits, aluminum offers substantial cost savings. For smaller branch circuits (AWG 10 and below), copper is almost universally preferred for reliability and code compliance.
Frequently Asked Questions
What AWG wire size do I need for 20 amps?
For a standard 20-amp circuit at 120V, AWG 12 copper wire is the minimum required by the NEC. For runs longer than 50 feet, consider AWG 10 to reduce voltage drop.
How do I calculate voltage drop in a wire?
Voltage drop equals (2 x current x distance x resistance per unit length) for single-phase circuits. This calculator does it automatically — enter your current, voltage, distance, and it shows the exact drop.
What is the difference between AWG and mm² wire sizes?
AWG (American Wire Gauge) is used in North America, while mm² (cross-sectional area) is the international standard. AWG 12 equals approximately 3.31 mm², and AWG 10 equals about 5.26 mm². This calculator converts between both systems.
Can I use aluminum wire instead of copper?
Yes, but aluminum has about 61% the conductivity of copper. You typically need to go one or two AWG sizes larger with aluminum to match copper performance. Aluminum is cost-effective for large feeder cables (AWG 4 and above).
What is acceptable voltage drop for a residential circuit?
The NEC recommends no more than 3% voltage drop on branch circuits and no more than 5% total from the service panel to the farthest outlet. This calculator defaults to 3% but allows adjustment.
What does wire ampacity mean?
Ampacity is the maximum current a conductor can carry continuously without exceeding its temperature rating. It depends on wire gauge, insulation type, ambient temperature, and installation method. NEC Table 310.16 provides standard ampacity values.
How does wire distance affect gauge selection?
Longer wire runs increase resistance and voltage drop. A 20-amp circuit that works fine with AWG 12 at 25 feet may need AWG 10 or AWG 8 at 100 feet to keep voltage drop under 3%.