Current density converter
Convert current per unit of conductor area between A/mm², A/cm², A/dm² and circular mils per amp.
That's about the same as a transformer winding. Through ordinary 2.5 mm² cable that is 7.5 A.
What it means
How hard is the conductor working?
Wiring figures are rough guidance only. Real cable ratings depend on insulation, bundling and air temperature, so follow your local wiring rules.
Every unit
Your current density in every unit
Learn
Three things worth knowing
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3 A/mm² runs cool
Transformer and motor windings are typically designed around 2 to 4 A/mm². Short household cable runs can carry more because they shed heat to the air.
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The circular mil
US wire is measured in circular mils: the area of a circle one thousandth of an inch across. It makes a round wire’s area simply its diameter in mils, squared, with no π.
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Double the area, not the diameter
Area grows with the square of the diameter, so a wire 1.4 times thicker already carries twice the current at the same density.
Shortcuts
Popular current density conversions
Background
About current density
Current density is current divided by the area it flows through. It is what heats a conductor: the same 20 A is harmless in a thick bar and dangerous in a thin wire.
Transformer designers aim for a few A/mm², electroplaters work in A/dm², and US electricians size wire in circular mils per amp, the same idea turned upside down.