Free · Electrical networks

Wire Gauge Diameter, Area and Reference Resistance

Compare 44 AWG and 57 SWG sizes, circular cross-section and nominal resistance per length using eight reference materials or custom resistivity.

Formula & worked example
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How to use this calculator

Enter the known values in the units shown. Results update as you type.
Where results are editable, change one to solve backwards. Lock a value to hold it fixed.
Use the worked example to check the method. Reset restores the starting fields.

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Formula and method

AWG 36 has defining diameter 0.127 mm. SWG 12 has nominal diameter 2.6416 mm (104 mil). The two gauge systems use different size definitions.

AWG diameter = 0.127 mm × 92^((36−AWG)/39); A = πd²/4; resistance per length = ρ/A

Worked example

Enter these known values and leave the other values blank.

Gauge type: American Wire Gauge (AWG)
American wire gauge: 36 AWG
Reference material: see grade and temperature scope: Copper
Nominal or custom resistivity: 0.0000000168 Ω ⋅m

Diameter: 0.127 mm
Cross-sectional area: 0.012668 mm²
Resistance per length: 1326.2 Ω/ km

Assumptions and limitations

Gauge selectors retain the captured locks. The AWG algebraic inverse is not a promised interactive diameter-to-gauge selector. Clearing an SWG preset retains its current diameter for manual editing; replace that value explicitly, or unlock the diameter to solve it from an entered area.
Solid circular conductor geometry. Diameter, area and resistance per length are geometric/reference calculations; allowable current, temperature rise, insulation, stranding and AC skin effect are not modeled.
All 44 AWG choices retain the NBS defining geometric progression. All 57 SWG choices retain the captured nominal table rounding except SWG 12, corrected to the primary 104 mil definition. Other SWG values may differ slightly from an exact inch conversion because of retained decimal rounding.
Silver, copper, gold, aluminum, nickel and nichrome use nominal educational 20°C resistivity references. Nichrome alloy composition and nickel grade can change actual values; these presets are approximate references, not measurements of every grade.
Carbon steel represents the cited AISI 1010 cold-drawn data. Electrical steel represents JFE JG CORE grades with typical 46 μΩ cm resistivity; other grades differ. The manufacturers do not specify a temperature for those rows, so they are not certified 20°C values.
Custom accepts a measured or specified nonnegative resistivity in the selected compound units. Zero represents an ideal zero-resistivity limit, not an ordinary metal operating condition.

Common questions

Can I use a measured diameter instead of an SWG preset?

Clear the SWG selection, then edit the retained circular diameter. The prior value stays until you replace it. To calculate diameter from area, unlock diameter before entering the known area. This does not automatically select a named SWG or AWG gauge.

Are AWG and SWG interchangeable?

No. Select the actual standard before choosing the gauge. The same gauge number generally has different diameters under the two systems.

Does this calculate a safe current rating?

It calculates geometry and reference resistance per length. A current rating also depends on operating temperature, insulation, installation and applicable electrical requirements.

References

NBS Handbook 100 Table 15 defines SWG12 as 104 mil = 2.6416 mm. The captured 2.632 mm falls outside its own rounding precision. Correct that cell and all original keyed aliases, retaining the other 56 rounded SWG rows and every choice identity. A circular conductor requires positive diameter and cross-section. Negative diameter otherwise produces a positive squared area; zero cross-section makes resistance per length undefined. Retain nonnegative resistivity, including a declared ideal zero-resistivity endpoint.

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