AWG Wire Gauge Calculator: Diameter, Area, Resistance and the Nearest Metric Size

AWG sizes, diameters, areas and resistance.

Calculated from standard textbook formulas, with every step shown. The formulas are fixed, so the working does not need checking: what matters is the numbers you type in. Use these calculators only if you are competent to choose the inputs (loads, material strength, dimensions, supports) and check your units and assumptions. For learning and checking your own working: design and sign-off are for a qualified engineer. Drafting Central does not store the numbers you type.

How this calculator works

Choose whether you know the AWG number, the diameter or the area, and enter it.

Enter the length and the temperature of the wire.

The calculator gives the AWG, the diameter in mm and mil, the area in mm2 and circular mils, and the resistance.

Formulas used

  • d = 0.127\times92^{(36 - n)/39}\,\mathrm{mm}
  • A = \frac{\pi d^2}{4}
  • R = \frac{\rho}{A}

Worked example

With the default numbers in the calculator above:

  1. AWG number: 14 (14)
  2. Diameter: 1.6277 mm (64.084 mil)
  3. Cross-section area: 2.0809 mm2 (4106.8 circular mils)
  4. Resistance of copper per metre at that temperature (resistivity 1.724e-8 ohm m at 20 C, rising 0.393 percent per degree): 8.2848 ohm per km (2.5252 ohm per 1000 ft)
  5. Resistance of the length you gave: 0.82848 ohm (828.48 milliohm)
  6. Nearest standard metric cable size that is at least as large: 2.5 mm2

Change the numbers in the calculator to see the full working, every step, for your own case.

A second worked example

A different case, with these numbers: What you know The area in mm2; The AWG number, the diameter in mm, or the area in mm2 2.5.

  1. AWG number: 13.21 (13.21, between two standard sizes)
  2. Diameter: 1.7841 mm (70.241 mil)
  3. Cross-section area: 2.5 mm2 (4933.9 circular mils)
  4. Resistance of copper per metre at that temperature (resistivity 1.724e-8 ohm m at 20 C, rising 0.393 percent per degree): 6.896 ohm per km (2.1019 ohm per 1000 ft)
  5. Resistance of the length you gave: 0.6896 ohm (689.6 milliohm)
  6. Nearest standard metric cable size that is at least as large: 2.5 mm2

Common questions

What is the diameter of 14 AWG wire?

About 1.63 mm, with an area of 2.08 mm2.

Which metric size is closest to 12 AWG?

12 AWG is 3.31 mm2, so 4 mm2 is the nearest metric size that is at least as large.

Why does a higher AWG number mean thinner wire?

The gauge counts the number of drawing steps. Each step makes the wire thinner.

Related calculators

Got a question about this? Ask an engineering question and get a plain-language answer with references.

Further reading: The ASTM B258 definition of AWG sizes. Copper resistivity at 20 C. Current ratings come from the wiring rules, not from this tool.

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