Wire Size and Cable Cross-Section Calculator
Convert wire and cable sizes between American Wire Gauge (AWG), metric cross-sectional area in mm2, and kcmil/MCM. This wire size calculator also derives equivalent solid-conductor diameter, copper resistance, the nearest standard AWG size, and an estimated maximum current for a chosen current density.
Convert AWG, mm2, and kcmil
The current value is an engineering estimate calculated as cross-sectional area times the selected current density. It is not a code-compliant ampacity rating. Insulation temperature, ambient temperature, bundling, installation method, conductor material, allowable voltage drop, and local electrical standards can require a substantially lower current.
Metric and AWG Wire Size Table
| Standard | Wire size | Diameter (mm) | Area (mm2) | Nearest AWG | Resistance (Ω/km) | Est. max current (A) | 100% skin depth |
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AWG Calculator Formulas
AWG is logarithmic. For gauge number \(n\), including negative numbers for 2/0 and larger sizes, the ideal solid-wire diameter is
\[d_{in}=0.005\cdot92^{\frac{36-n}{39}}.\]
The cable cross section follows from \(A=\frac{\pi}{4}d^2\). In the reverse direction, the calculator finds the nearest standard AWG size from the metric area. This makes it usable as an AWG to mm2 calculator, a mm2 to AWG converter, and a kcmil converter.
One kcmil, historically also called one MCM, corresponds to approximately \(0.506707\,\mathrm{mm}^2\). Copper resistance at \(20\,^\circ\mathrm{C}\) is estimated from
\[R_{km}\approx\frac{17.241}{A_{mm^2}},\]
while the adjustable current estimate uses
\[I_{est}=J\,A,\]
where \(J\) is the selected current density in amperes per square millimeter. For an actual installation, the final conductor choice must also satisfy the applicable ampacity table and voltage-drop limit.
Skin Depth and Maximum Frequency
The frequency result assumes a solid, round, nonmagnetic copper conductor at 20 C. It is the frequency at which the classical skin depth \(\delta\) equals the conductor radius \(r\):
\[\delta=\sqrt{\frac{\rho}{\pi f\mu_0}}=r \quad\Longrightarrow\quad f=\frac{\rho}{\pi\mu_0r^2}.\]
This is a geometric skin-effect reference, not a hard operating-frequency limit. Stranding, plating, proximity effect, waveform harmonics, and acceptable AC resistance determine practical high-frequency use.
How Many Amps Can a 0.3 mm2 Wire Carry?
With the calculator's default current density of \(6\,\mathrm{A/mm^2}\), a 0.3 mm2 copper wire gives an estimated current of \(0.3\cdot6=1.8\,\mathrm{A}\). There is no universal 0.3 mm2 wire amp rating: short open-air chassis wiring may use a higher current density, while bundled or enclosed wiring may require a lower value.
Common Cable Cross Sections and Amp Estimates
At \(6\,\mathrm{A/mm^2}\), the same estimate gives 4.5 A for 0.75 mm2, 9 A for 1.5 mm2, 15 A for 2.5 mm2, and 36 A for 6 mm2. These values answer common searches such as "1.5 mm2 what amp" or "2.5 mm2 cable amps" only under that stated current-density assumption; applicable wiring codes remain authoritative.