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Wire length and area converter

Two converters an apprentice reaches for when a drawing, a spool or a spec sheet speaks the other system: run length in feet or metres, and conductor size between AWG, kcmil, circular mils and mm².

Length follows the Imperial / Metric switch.

Run length (ft)

Feet—

Metres—

Inches—

Millimetres—

Conductor size — I have it in

AWG kcmil mm²

Gauge (e.g. 12 or 4/0)

AWG—

kcmil—

Circular mils—

mm²—

Diameter (solid)—

Areas are from the AWG definition for a solid round wire; stranded conductor areas in code tables differ slightly — check your code book. A converted size is not a permitted substitute.

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How it works

Length is one exact number: an international foot is 0.3048 m, by definition. Feet to metres, multiply by 0.3048; metres to feet, divide by it (or multiply by about 3.281). An inch is exactly 25.4 mm.

AWG is a geometric series: #36 is defined as 0.005" across and 4/0 as 0.46", with 39 equal ratio steps between them. So the diameter of gauge n is 0.005 × 92^{(36 − n) / 39} inches. Every three gauges smaller roughly halves the area; every six roughly halves the diameter. The area in circular mils is the diameter in mils squared, and one circular mil is π/4 × 0.0254² ≈ 0.000507 mm², so 1 kcmil ≈ 0.507 mm².

Worked examples

A 50 m run in feet

50 ÷ 0.3048 = 164.04 ft — call it 164 ft.
The other way: 100 ft × 0.3048 = 30.48 m.

#12 in circular mils and mm²

Diameter: 0.005 × 92^{(36 − 12) / 39} = 0.005 × 92^0.6154 ≈ 0.0808 in (2.05 mm).
Area: 80.8 mils squared ≈ 6,530 cmil.
In mm²: π/4 × 2.053² ≈ 3.31 mm².

250 kcmil in mm²

250 kcmil = 250,000 cmil.
× 0.0005067 mm² per cmil = 126.7 mm². It is bigger than 4/0 (211.6 kcmil), which is why it has no gauge number.

Questions people ask

Is 2.5 mm² the same as #14 or #12?

Neither exactly. By area, #14 is about 2.08 mm² and #12 about 3.31 mm², so 2.5 mm² sits between them — and metric and AWG conductors are not interchangeable one-for-one. Which size a circuit needs is a code-book question (ampacity, temperature, installation), not a conversion.

Why does my code book give a slightly different area?

This converter uses the definition of the gauge for a solid round wire. Real conductors — especially stranded ones — are made to standards whose areas differ a little from the pure formula. For anything that matters (fill, lug range, ampacity), use the figure in your code book or the maker’s data.

What is a kcmil?

A thousand circular mils. A circular mil is the area of a circle one mil (a thousandth of an inch) across, so a wire’s area in circular mils is just its diameter in mils, squared. Above 4/0, conductor sizes are named in kcmil — 250, 350, 500 — instead of gauge numbers. Older prints write it MCM.

Conductors and insulation — the lesson behind this tool.
Trade math refresher — the lesson behind this tool.
Metric ↔ imperial — the conversions by hand.
Voltage drop calculator — where the run length goes next.
Ampacity — why size is not the whole story.
Fraction / decimal / mm sheet

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