Convert Amperes per Square Inch to Amperes per Square Mil
Ampere per Square Inch (A/in²) to Ampere per Square Mil (A/mil²) surface current density conversion — enter any value below to get an instant result, or use the table for common values.
Results from this calculator are estimates provided for general informational purposes only, based on formulas, rates, and standards commonly accepted as of 2026. Figures may differ slightly from other calculators or professional sources due to rounding methods, differing assumptions, or regional regulations, and rules may change over time. Always consult a qualified professional — such as a financial advisor, healthcare provider, or other relevant specialist — before making decisions based on these results.
Result
1 A/in² = 1E-06 A/mil²
1 Ampere per Square Inch = 1E-06 Amperes per Square Mil
1 Ampere per Square Mil = 1000000 Amperes per Square Inch
1 A/in² in every supported unit
Conversion chart: Ampere per Square Inch to Amperes per Square Mil
Conversion table
| Ampere per Square Inch (A/in²) | Ampere per Square Mil (A/mil²) |
|---|---|
| 0.01 A/in² | 1E-08 A/mil² |
| 0.1 A/in² | 1E-07 A/mil² |
| 1 A/in² | 1E-06 A/mil² |
| 2 A/in² | 2E-06 A/mil² |
| 3 A/in² | 3E-06 A/mil² |
| 5 A/in² | 5E-06 A/mil² |
| 10 A/in² | 1E-05 A/mil² |
| 20 A/in² | 2E-05 A/mil² |
| 50 A/in² | 5E-05 A/mil² |
| 100 A/in² | 0.0001 A/mil² |
| 1000 A/in² | 0.001 A/mil² |
Ampere per Square Inch (A/in²)
Definition: The US customary version of current density, expressing current per square inch of cross-sectional area rather than per square meter.
History: Used historically in American and British electrical engineering practice before full SI unification, particularly in wire and cable ampacity tables that specified conductor cross-sections in inches.
Current use: Occasionally seen today in legacy US electrical code documentation and older cable ampacity references that predate metric-only specification.
Ampere per Square Mil (A/mil²)
Definition: Current density expressed per square mil — one mil being one-thousandth of an inch — an extremely fine imperial area unit suited to very thin conductors.
History: Rooted in the American wire and electronics manufacturing industry's long-standing use of the "mil" (thousandth of an inch) to describe thin conductors, wire insulation thickness, and printed-circuit-board copper thickness.
Current use: Still used today in PCB design for specifying maximum allowable current density in copper traces, often quoted as amps per square mil in IPC-2152-style trace-width and current-carrying-capacity guidance.
Supported Units
| Unit | Symbol | In Ampere/Square Meter |
|---|---|---|
| Ampere per Square Meter | A/m² | 1 A/m² |
| Ampere per Square Centimeter | A/cm² | 10000 A/m² |
| Ampere per Square Inch | A/in² | 1550.0031 A/m² |
| Ampere per Square Mil | A/mil² | 1.55E+09 A/m² |
| Ampere per Circular Mil | A/cmil | 1.97353E+09 A/m² |
| Abampere per Square Centimeter | abA/cm² | 100000 A/m² |
About These Parameters
- Value
- The surface current density value you want to convert, expressed in the "From" unit. Accepts decimals, and can represent anything from a PCB copper trace's amps-per-square-mil rating to an electroplating bath's amps-per-square-centimeter setting.
- From Unit
- The unit your input value is currently measured in — a modern calculation's ampere-per-square-meter figure, an electroplating spec's amps-per-square-centimeter rating, or an AWG wire table's amps-per-circular-mil convention.
- To Unit
- The unit you want the result converted into. Use the swap button to flip From and To instantly, which is handy when translating a PCB or wire-gauge ampacity figure into SI ampere per square meter or vice versa.
How Surface Current Density Conversion Works
The Formula
Every unit here is defined by a fixed multiplier relative to ampere per square meter. To convert a value from one unit to another:
result = value × (factor of "From" unit ÷ factor of "To" unit)
For Ampere per Square Inch → Ampere per Square Mil: multiply by 1E-06. For example, 1 A/in² × 1E-06 = 1E-06 A/mil².
Current Density and Ohm's Law
Surface current density (J) is the local, per-area version of electric current, related to the electric field (E) and a material's conductivity (σ) by the microscopic form of Ohm's law, J = σE. It matters because two wires carrying the identical total current in amperes can behave completely differently depending on their cross-sectional area — a thin wire with high current density runs hotter and is more prone to resistive (I²R) heating damage than a thick busbar carrying the same total current spread across far more copper. This is why every conductor, from a PCB trace to a power transmission cable, is ultimately rated by its safe current density, not just its total current-carrying number.
Mils, Square Mils, and Circular Mils
American wire and electronics manufacturing traditionally measures very small conductor dimensions in mils (thousandths of an inch) rather than millimeters. A square mil is simply a mil-by-mil square, used in PCB design for specifying copper trace current density under guidance like IPC-2152. A circular mil, by contrast, is the area of a circle exactly one mil in diameter (π/4 times a square mil) — the standard cross-section unit for round wire in American Wire Gauge (AWG) tables, since round wire is naturally specified by diameter rather than by an equivalent square area. Both units let American electrical engineers work directly in the inch-based dimensions their wire and board specifications are already written in.
Example
A surface current density of 1 A/in² equals 1E-06 A/mil². For scale, PCB copper traces are commonly designed for roughly 0.02-0.05 amps per square mil depending on trace thickness and allowable temperature rise, while typical copper house wiring safely carries on the order of a few hundred amps per square centimeter.
Frequently Asked Questions
How many Amperes per Square Mil are in 1 Ampere per Square Inch?
1 Ampere per Square Inch (A/in²) equals exactly 1E-06 Amperes per Square Mil (A/mil²).
What is the difference between current and current density?
Current (measured in amperes) is the total flow of charge through an entire conductor, regardless of its thickness. Current density (measured in amperes per square meter or similar) is current per unit of cross-sectional area, which is what actually determines how hot a conductor runs and how much material is needed to carry a given current safely.
What is a circular mil and why is it used for wire gauge?
A circular mil is the cross-sectional area of a circle exactly one mil (one-thousandth of an inch) in diameter. Because round wire is naturally specified by its diameter, American Wire Gauge (AWG) tables use circular mils as the standard area unit rather than square inches or square millimeters, making wire cross-section and ampacity easy to look up directly from gauge number.
Why do PCB designs use amps per square mil?
Printed circuit board copper traces are extremely thin, so their thickness and width are conventionally measured in mils (thousandths of an inch). Expressing maximum safe current density in amps per square mil, as guidance like IPC-2152 does, lets PCB designers directly size trace widths from a target current without converting to metric units first.
What is the abampere per square centimeter unit used for?
Abampere per square centimeter is a CGS-electromagnetic-system current density unit, combining the abampere (10 amperes) with the CGS area unit of square centimeters. It is essentially obsolete today, appearing mainly in classic electromagnetism textbooks that work examples entirely within the Gaussian/CGS unit system rather than SI.