American Wire Gauge is a standardized wire size system where smaller numbers indicate thicker wire. AWG 0000 (4/0) is about 11.7 mm diameter, while AWG 40 is just 0.08 mm. Each 6-AWG decrease doubles the cross-sectional area.

Why does wire length matter?

Longer wires have more resistance (R = rho × L/A). The voltage drop across the wire increases with length, reducing the voltage available at the load. For long runs, thicker wire or higher source voltage is needed.

What is voltage drop and why does it matter?

Voltage drop is the voltage lost across the wire resistance. Excessive drop causes dim lights, slow motors, and equipment malfunction. The National Electrical Code recommends no more than 3% drop for branch circuits.

Is copper or aluminum wire better?

Copper has lower resistivity (better conductivity) and is easier to connect. Aluminum is lighter and cheaper but requires larger gauges for the same current and special connectors to prevent corrosion at junctions.

How does temperature affect wire ampacity?

Wire ampacity (maximum safe current) decreases in hot environments because the insulation has a maximum temperature rating. In a 40 C attic versus a 30 C basement, the same wire can safely carry about 10-15% less current.

Wire Gauge Calculator

Convert AWG to mm diameter

AWG Wire Gauge

Enter AWG number

AWG Number

Formula

d(mm) = 0.127 x 92^((36-AWG)/39)

What Is Wire Gauge?

Wire gauge is a standardized system for specifying the diameter of electrical wire. The American Wire Gauge (AWG) system is widely used in North America and assigns numbers to wire sizes — counterintuitively, a lower gauge number means a thicker wire. AWG 0000 (4/0) is the thickest, while AWG 40 is extremely fine.

Choosing the correct wire gauge is critical for safety and performance. A wire that is too thin for its current load will overheat, potentially causing fires. The wire gauge determines the conductor's resistance per foot, its current-carrying capacity (ampacity), and how much voltage drops over a given length. This calculator converts AWG to physical dimensions and current ratings.

How to Use This Calculator

Enter the AWG gauge number (e.g., 12, 14, 18) or select from the dropdown.
The calculator displays the wire diameter in inches and millimeters.
View the cross-sectional area in circular mils (kcmil) and square millimeters (mm²).
See the recommended maximum current (ampacity) for the selected gauge.

Formula & Explanation

Diameter (in) = 0.005 × 92^((36 - AWG) / 39)
Area (mm²) = π/4 × (diameter in mm)²
Resistance (Ω/km) = ρ × 1000 / Area

ρ (copper resistivity) = 1.724 × 10⁻⁸ Ω·m. The AWG formula gives exact diameters for standard gauges. Ampacity depends on insulation type and installation conditions — values shown are for 60°C insulation in free air.

Worked Examples

Example 1 — AWG 12 (Household Wiring)

AWG 12: diameter = 2.053 mm, area = 3.31 mm², ampacity ≈ 20 A. Standard for 20 A circuits in US homes.

Example 2 — AWG 14 (Lighting Circuits)

AWG 14: diameter = 1.628 mm, area = 2.08 mm², ampacity ≈ 15 A. Common for 15 A lighting and outlet circuits.

Example 3 — AWG 24 (Signal Wire)

AWG 24: diameter = 0.511 mm, area = 0.205 mm², ampacity ≈ 0.577 A. Typical for telephone, audio, and low-voltage signal wiring.

Frequently Asked Questions

Why does a lower AWG number mean a thicker wire?▾

The AWG system originates from wire drawing — the number of drawing passes required to reach the final diameter. More passes produce thinner wire, so a higher AWG number means more draws and a finer wire.

What AWG is standard household wiring?▾

In North America, most 15 A circuits use AWG 14, 20 A circuits use AWG 12, and 30 A circuits (dryers, A/C) use AWG 10. Always verify with local electrical codes before wiring.

What is the difference between solid and stranded wire?▾

Solid wire has a single conductor; stranded wire has multiple smaller wires twisted together. Stranded wire is more flexible and fatigue-resistant, making it better for applications with movement. Solid wire is easier to splice and cheaper.

How does wire length affect voltage drop?▾

Resistance increases with length, causing more voltage drop across a long run. For critical loads, calculate the total round-trip distance and check that the drop stays below 3–5% of the supply voltage. Upsize the gauge for longer runs.

Can I use AWG wire outside North America?▾

In most of the world, wire is sized by cross-sectional area in mm² (IEC standard). AWG 12 ≈ 3.3 mm², AWG 14 ≈ 2.1 mm², AWG 18 ≈ 0.82 mm². This calculator shows both for easy cross-reference.