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.
Les sections viennent de la définition AWG pour un fil rond massif; les sections des conducteurs toronnés dans les tableaux du Code diffèrent légèrement — vérifiez votre Code. Une grosseur convertie n’est pas un substitut autorisé.
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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 × 920.6154 ≈ 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 fréquentes
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.
Voir aussi
- 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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