Wire Gauge Calculator (AWG ↔ mm²)
Convert American Wire Gauge (AWG) to diameter and cross-sectional area in mm², with a rough guide to how much current the wire can safely carry. Essential when working across US and metric conventions.
How to use this calculator
- Enter the AWG number — remember lower numbers mean thicker wire.
- Press Convert for diameter, area in mm², and a rough current guide.
- Use the conservative ampacity for in-wall power wiring, never the generous one.
Formula used
The AWG scale is logarithmic and inverted — bigger numbers are thinner wires, and every 3-gauge step roughly halves or doubles the cross-sectional area. This geometric relationship is why the conversion formula uses a power of 92.
Example calculation
AWG 12 = 2.05 mm diameter = 3.31 mm² — common for household power circuits, good for roughly 20 A in typical wiring.
AWG 15 (three steps thinner) is about half the area (~1.65 mm²); AWG 9 (three steps thicker) is about double.
Why gauge numbers run backwards
American Wire Gauge is counter-intuitive by design: the number counts how many times the wire was drawn through progressively smaller dies, so more drawing means thinner wire and a higher number. The scale is geometric — each 3-gauge change roughly doubles or halves the cross-sectional area, and each 6-gauge change changes the diameter by about 2×.
Cross-sectional area is what actually matters, because it determines resistance and therefore how much current a wire can carry before overheating. But real-world ampacity depends on far more than the wire itself — insulation temperature rating, whether it's bundled or in free air, ambient temperature and run length all matter, which is why the figures here are guides and local wiring codes are the authority for anything mains-powered.
Why use this calculator?
- Convert between US AWG specs and metric mm² cable ratings.
- Get a sanity-check current capacity for wire selection.
- Understand the backwards gauge scale with the doubling rule.
Frequently asked questions
What does AWG mean and why is lower thicker?
American Wire Gauge — the number reflects how many times the wire was drawn thinner, so higher numbers are thinner wires. AWG 10 is thick (power circuits), AWG 24 is thin (signal wiring).
How do I convert AWG to mm²?
Compute the diameter with 0.127 × 92^((36−AWG)/39) mm, then area = π × (diameter/2)². AWG 12 works out to about 3.3 mm². The calculator does this instantly.
How much current can a wire carry?
It depends on the wire's area plus insulation rating, installation method, temperature and length — there's no single answer from gauge alone. The figures here are rough guides; for mains wiring always follow local electrical codes and cable ratings.