CalcKit
Surface Current Density Converter
This converter is for current density: the electric current through each unit of a conductor's cross-section, J = I / A. Its SI unit is the ampere per square meter (A/m²). It is how wires, busbars and PCB tracks are sized, since the current density decides how hot a conductor gets.
Wiring is usually sized in amperes per square millimeter: 1 A/mm² = 1,000,000 A/m², which is 100 A/cm². US wire tables use circular mils (cmil), the area of a circle one thousandth of an inch across.
How to convert current density units
Type a value into any field, and every other unit is calculated at once. For example, a copper wire carrying 4 A/mm², which is 400 A/cm²:
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In A/m²: multiply by 10,000.
400 * 10,000 = 4,000,000 A/m² -
In A/in²: multiply by 6.4516.
400 * 6.4516 = 2,581 A/in² -
In circular mils per ampere, the form US wire tables use: divide 1 by the value in A/cmil.
1 / 0.002027 = 493cmil/A
Common conversions
| Value | Equals |
|---|---|
| 1 A/cm² | 10,000 A/m² |
| 1 A/m² | 0.0001 A/cm² |
| 1 A/in² | 1,550 A/m² |
| 1 A/cm² | 6.4516 A/in² |
| 1 A/cmil | 197,353 A/cm² |
| 1 abA/cm² | 10 A/cm² |
Current density units
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Ampere per square meter (A/m²): The standard unit of current density, where one Ampere of current flows through one square meter of area.
Conversion factors: 1 A/m² = 1 A/m² (Base Unit) -
Ampere per square centimeter (A/cm²): This unit expresses current density in Amperes per square centimeter.
Conversion factors: 1 A/cm² = 10,000 A/m² -
Ampere per square inch (A/in²): Current density measured in Amperes per square inch.
Conversion factors: 1 A/in² ≈ 1,550 A/m² -
Ampere per square mil (A/mi²): Current density expressed in Amperes per square mil, where one mil is equal to one-thousandth of an inch.
Conversion factors: 1 A/mi² ≈ 1,550,003,100 A/m² -
Ampere per circular-mil (A/cmil): This unit represents current density in Amperes per circular mil, where a circular mil is the area of a circle with a diameter of one mil (0.001 inches).
Conversion factors: 1 A/cmil ≈ 1,973,525,242 A/m² -
Abampere per square centimeter (abA/cm²): The abampere is a unit of electromagnetic current in the CGS system. Abampere per square centimeter expresses current density in abamperes per square centimeter.
Conversion factors: 1 abA/cm² = 10 A/cm² = 100,000 A/m²
Frequently asked questions
How much current density can a copper wire carry?
It depends on the cooling and the allowed temperature rise. As a rough guide, building wiring runs at about 2–6 A/mm², transformer windings at 1.5–4 A/mm², and short PCB tracks higher. Always check the wiring standard that applies.