Wire size calculator

Minimum area for the entered voltage-drop limit = 2 × length × current × resistivity ÷ allowed voltage drop.

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One-way length (meters)

Current (amps)

More inputs and assumptions

Maximum voltage drop (volts)

Resistivity at operating temperature (Ω·mm²/m)

Answer

…

Minimum area for the entered voltage-drop limit = 2 × length × current × resistivity ÷ allowed voltage drop.

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Precision and calculation record

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Formula and assumptions

Two-wire DC or resistive single-phase voltage-drop sizing only. This does not calculate thermal ampacity or choose a code-compliant gauge. The resistivity is your input; the default is an illustrative input, not a material specification. Choose a conductor that also meets temperature, installation, fault-protection and local-code requirements.

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Updated 2026-09-29

Using Wire size calculator

Minimum area for the entered voltage-drop limit = 2 × length × current × resistivity ÷ allowed voltage drop.

Next: Voltage drop calculator

Next: Resistance calculator

A worked example

For one-way length (meters) = 20, current (amps) = 10, maximum voltage drop (volts) = 3, resistivity at operating temperature (ω·mm²/m) = 0.017241, area for voltage-drop limit (mm²) = 2.2988.

Before you use the result

Example results for one-way length (meters)

These examples use Current (amps): 10; Maximum voltage drop (volts): 3; Resistivity at operating temperature (Ω·mm²/m): 0.017241. They are reference calculations, not recommended settings.

One-way length (meters)	Area for voltage-drop limit (mm²)
10	1.1494
20	2.2988
40	4.5976

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