CONDUCTORS · CALCULATOR

Conductor sizing calculator

Free conductor sizing calculator: get minimum area (drop only) from voltage, current, one-way cable length and resistivity at operating temperature.

Written by Chameera Sampath · Not yet reviewed by a licensed electrician. See the methodology.

US (NEC) only · NFPA 70 / NEC — locally adopted editionDefaults are US values. Verify the locally adopted NEC edition and project data.Official reference ↗

Project inputs

Measurements

Voltage

Current

One-way cable length

Resistivity at operating temperature

Ω·cmil/ft

Allowed voltage drop

Supply

Resistivity starting point:Override with project temperature / manufacturer data.

Updates as inputs change. Unit changes preserve the same physical values.

THE MATH BEHIND THE ANSWER

Method & assumptions

Amin = k × I × ρ × Leffective / (V × limit / 100)

Choose the next available size and separately check ampacity, fault withstand and terminals.

Results do not check every aspect of an electrical installation. The calculators follow US (NEC) practice only; a regional preset changes defaults such as voltage and units, and no result certifies NEC compliance.

Sources and validation →

Worked example

Voltage: 120 V · Current: 20 A · One-way cable length: 100 ft · Resistivity at operating temperature: 12.9 Ω·cmil/ft · Allowed voltage drop: 3 % · Supply: Single phase

Minimum area (drop only): 14.333 kcmil

This example uses the stated inputs; results for the entered values appear above.

Explore the conductors branch →See the related electrical concepts →

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