Calculate the wire gauge for a DC circuit

At low voltage, a wire that is too thin loses volts before the device. Enter the current and the circuit length: the tool suggests the smallest gauge that keeps the voltage drop under the limit.

A calculation aid only, not a compliance check. The gauge must also carry the current according to its insulation and how it is run, and each circuit must be protected by a fuse matched to the wire. If in doubt, have the installation checked by a qualified person.

Draw the layout in Planimonde

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How it is calculated

The length to enter is the round trip: the positive wire plus the negative wire. For a device 4 m from the battery, count 8 m.

Minimum cross-section = resistivity of copper (0.0175 Ω·mm²/m) × length × current ÷ allowed voltage drop in volts. The tool picks the first AWG size whose cross-section is at least that, then recomputes the actual drop.

3% is the usual limit for sensitive circuits (electronics, lighting, refrigerator); 10% is tolerated for loads that can take it. The calculation only considers voltage drop.

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