AWG Wire Calculator
The diameter, cross-section and resistance of an American Wire Gauge size, from 4/0 to 40, or the nearest gauge to a diameter or a mm² area.
Result
Diameter: 0.08081 in
Solid round conductor at 20 °C. It gives no current rating: ampacity and breaker size are set by the electrical code and the installation, and local codes vary.
- Diameter in mils (thousandths of an inch)
- 80.8
- Cross-section area
- 3.309 mm²
- Area in circular mils
- 6,530
- The diameter in mils, squared: the unit US wire tables use.
- Resistance per 1,000 ft at 20 °C
- 1.588 ΩEstimate
- Resistance per km at 20 °C
- 5.211 ΩEstimate
- Resistance of that length at 20 °C
- 0.1588 ΩEstimate
https://calcgallery.com/electronics/awg-wire-calculator/
Results come from the published equations applied to the values you enter. They are not electrical design, conductor sizing, laboratory safety or medical guidance. Weather indices describe a standard person in standard conditions and are not a forecast. Where codes apply, local rules vary and must be checked. Read the full disclaimer
How to use the AWG Wire Calculator
- Choose whether you are starting from a gauge, a measured diameter or a metric cross-section in mm².
- Pick the gauge, or type the diameter of the bare conductor or its area.
- Choose copper or aluminium, and enter a length if you want the resistance of a particular piece of wire.
- Read the diameter, the area in mm² and circular mils, and the resistance per 1,000 ft, per km and for your length.
The gauge formula
American Wire Gauge fixes two sizes and a rule. ASTM B258 sets 4/0 at 460 mils (0.460 in) and 36 AWG at 5 mils (0.005 in), and the sizes between them form a geometric series, so every step is the same ratio. With 1/0 as 0 and 4/0 as −3:
diameter = 0.005 in × 92^((36 − n) ÷ 39)n = 36 − 39 × log₉₂(diameter ÷ 0.005 in)area = π × diameter² ÷ 4Going the other way, a measured diameter or a metric area gives a gauge number that is usually not a whole number. The page leads with the smallest standard gauge that is at least as large as the size entered, with its area, because the nearest gauge can be a smaller conductor than the one you started from. It also rounds to the nearest gauge and shows its diameter, so you can see how close the match is.
Six gauge steps almost exactly halve the diameter, and three steps almost exactly halve the area. That is the shortcut behind rules of thumb like “10 AWG has twice the area of 13 AWG”.
Resistance
Resistance is resistivity times length divided by area. The page uses the International Annealed Copper Standard for copper and the resistivity of EC-H19 aluminium conductor, both at 20 °C and both from the site’s register of cited values. A conductor carrying current runs warmer, and its resistance rises by about 0.4% for every degree Celsius, so under load the figure here is a lower bound.
The length is one conductor from end to end. For the voltage lost in a circuit, where the current goes out and comes back, use the voltage drop calculator, which counts both conductors.
What this page does not do
It does not size a wire for a load. It gives no ampacity, breaker size or conduit fill, because those are set by electrical codes that vary by country and by jurisdiction. Local codes vary and must be checked. The sizes are for solid round wire: a stranded conductor of the same gauge has the same metal area but a larger outside diameter, and a measured stranded diameter will read as a thicker gauge than it is.
With your numbers
- Diameter = 0.005 in × 92^((36 − 12) ÷ 39) = 0.0808 in
- Area = π × d² ÷ 4 = 3.3088 mm²
- Resistance per km = resistivity ÷ area = 5.2108 Ω
Quick reference
Solid round conductor at 20 °C. It gives no current rating: ampacity and breaker size are set by the electrical code and the installation, and local codes vary.
| Example | Result |
|---|---|
| 14 AWG copper, 100 ft | Diameter: 0.06408 in |
| 12 AWG copper, 100 ft | Diameter: 0.08081 in |
| 10 AWG copper, 100 ft | Diameter: 0.1019 in |
| 4/0 aluminium, 100 ft | Diameter: 0.46 in |
| 22 AWG hook-up wire, 10 ft | Diameter: 0.02535 in |
| A 2 mm wire to its gauge | Smallest gauge at least this size (AWG): 12 |
| 2.5 mm² to a gauge | Smallest gauge at least this size (AWG): 13 |
| 1.5 mm² to a gauge | Smallest gauge at least this size (AWG): 15 |
| 35 mm², where the nearest gauge is smaller | Smallest gauge at least this size (AWG): 1 |
Where the numbers come from
The fixed figures this calculator relies on, and the published source each one was checked against. How the calculators are built and checked
2 sources
NBS Handbook 100, Copper Wire Tables (1966), p. 2: "0.017 241 ohm-mm2/meter at 20 °C, 1.7241 microhm-cm at 20 °C", https://nvlpubs.nist.gov/nistpubs/Legacy/hb/nbshandbook100.pdf
Used for
- Resistivity of annealed copper at 20 °C, the International Annealed Copper Standard: 1/58 Ω·mm²/m, 1.7241 µΩ·cm.
NBS Handbook 109, Aluminum Wire Tables (February 1972), Table 1, p. 5: EC-H19, 61% IACS, 0.028264 ohm-mm2/meter at 20 °C, https://nvlpubs.nist.gov/nistpubs/Legacy/hb/nbshandbook109.pdf
Used for
- Resistivity of EC-H19 aluminium conductor (61% IACS) at 20 °C: 0.028264 Ω·mm²/m.
Common questions about the AWG Wire Calculator
- How thick is 12 gauge wire?
- A solid 12 AWG conductor is about 0.0808 in, or 2.05 mm, across, with an area of about 3.31 mm². Stranded 12 AWG has the same copper area but is slightly wider over the strands, and the insulation adds more on top.
- Why do smaller gauge numbers mean thicker wire?
- The numbers once counted drawing steps: a wire pulled through more dies came out thinner and got a higher number. The gauge is now a fixed rule instead. 36 AWG is exactly 0.005 in, 4/0 is exactly 0.46 in, and the 38 sizes between them shrink by the same ratio at each step, the 39th root of 92, about 1.1229.
- What are 1/0, 2/0, 3/0 and 4/0?
- The sizes above 1 AWG, read as "one aught" to "four aught" and also written 0, 00, 000 and 0000. In the gauge formula they are 0, −1, −2 and −3, which is how this page converts them.
- How many amps can this wire carry?
- This page does not say, on purpose. The current a conductor may carry depends on its insulation temperature rating, how it is installed, how many conductors share a conduit, the air around it and the terminals it lands on. In the United States the National Electrical Code sets it; elsewhere a national wiring code does, and local rules can differ. Check the code that applies where the wire is installed, or ask a licensed electrician.
- How do I convert mm² to AWG?
- Choose "A cross-section area", type the metric size, and the page works out the diameter of a round conductor with that area, the smallest gauge at least that size and the gauge nearest to it. Metric sizes do not line up with gauges: 2.5 mm² falls between 13 and 14 AWG, so neither is an exact equivalent, and the continuous gauge number shows how far it sits from each. The nearest gauge can be the smaller one: 35 mm² is nearest to 2 AWG, which has less area than 35 mm², while 1 AWG is the smallest with at least as much.
- Why does aluminium have more resistance?
- Aluminium conducts about 61% as well as annealed copper, so the same size of aluminium conductor has roughly 1.6 times the resistance. That is why aluminium conductors are usually a size or two larger than copper ones doing the same job.