Wire Gauge Calculator (AWG to mm)
Diameter, area, and circular mils from AWG size.
What it does
American wire gauge numbers wire backwards: higher numbers mean thinner conductors, with each three steps roughly halving cross section. The ASTM definition pins diameter to 0.005 inches times 92 to the gauge power, which this page converts to millimeters.
The tool above takes any AWG from 0 to 40. It returns diameter, cross section area, and circular mils.
Doubling area needs three gauge steps down. Twelve AWG at 3.30 mm² doubles near 9 AWG, which is why extension cords jump sizes fast under heavy loads.
Ampacity lives in code tables, not this converter. Insulation rating, bundling, and ambient temperature decide safe current for a given size.
How to use
- Enter the AWG number from the jacket print.
- Read diameter for terminals and holes.
- Read mm² for metric breaker and lug matching.
- Check ampacity in code tables before loading.
Formula
- 92^...
- Geometric ladder: 39 steps span 92x diameter.
- 0.005 in
- Anchor: 36 AWG measures five thousandths.
- cmil
- Diameter in thousandths squared, the trade unit.
Stranded wire measures the same copper area with slightly larger overall diameter. Tables quote solid diameters as here.
Worked example
Example: 12 AWG
Common household branch circuit wire.
- Diameter: 0.005 x 92^(24/39) = 0.0807 in.
- Metric: 0.0807 x 25.4 = 2.05 mm.
- Area: pi/4 x 2.05² = 3.31 mm².
- Cmil: 0.0807² x 1,000,000 = 6,530 circular mils.
Reference table
| AWG | Diameter | Area | Typical use |
|---|---|---|---|
| 18 | 1.02 mm | 0.82 mm² | Thermostats, doorbells |
| 14 | 1.63 mm | 2.08 mm² | Lighting circuits |
| 12 | 2.05 mm | 3.31 mm² | Outlets, 20 A |
| 10 | 2.59 mm | 5.26 mm² | 30 A appliances |
| 6 | 4.12 mm | 13.3 mm² | Sub panels |
Limits
- Size only. Ampacity needs code tables.
- Solid diameters shown. Stranded runs slightly larger.
- Aluminum wire sizes differently for equal amps.
- Temperature ratings change everything downstream.
Common mistakes
- Reading bigger AWG as bigger wire.
- Matching metric lugs by diameter instead of area.
- Forgetting strands need proper terminals.
- Sizing by this page instead of ampacity tables.
- Mixing copper and aluminum without rated joints.
Try it yourself
Quick checks. Answers sit tucked under each question.
Diameter of 10 AWG?
0.005 x 92^(26/39) = 0.1019 in, which is 2.59 mm.
Area of 14 AWG?
1.63 mm across gives pi/4 x 1.63² = 2.08 mm².
Questions
What size is 12 AWG in mm?
2.05 mm diameter, 3.30 mm² area.
Why do numbers run backwards?
History: gauges counted drawing dies. More draws meant thinner wire.
How many amps can 12 AWG carry?
Twenty amps on common 60-75°C branch circuits per code tables.
Stranded or solid?
Same copper area. Stranded flexes for cords, solid holds shape in walls.
What is a circular mil?
Area of a thousandth inch circle. Wire trade totals in thousands of them.
Can I use metric wire on AWG lugs?
Match cross section area closely with rated terminals, never force fits.