ac cable size calculator

Why AC cable sizing matters

Choosing the right AC cable size is one of the most important electrical design decisions. If a cable is too small, you can get overheating, reduced equipment life, nuisance tripping, poor motor performance, or even fire risk. If it is too large, installation costs increase unnecessarily.

A practical cable sizing method balances two key limits:

• Current carrying capacity (ampacity): the cable should safely carry load current.
• Voltage drop: the cable should keep voltage loss low enough for proper operation.

How this calculator works

This AC cable size calculator estimates the minimum cross-sectional area in mm² and then rounds up to the nearest standard cable size. It uses your selected system type, material, line voltage, load current (or power), cable length, and allowable voltage drop.

Voltage drop formulas used

System	Formula for required area A (mm²)
Single phase	A = (2 × I × ρ × L) / Vdrop
Three phase	A = (√3 × I × ρ × L) / Vdrop

Where:

• I = load current (A)
• ρ = conductor resistivity (Copper ≈ 0.0175, Aluminum ≈ 0.0282 Ω·mm²/m)
• L = one-way run length (m)
• V_drop = permitted voltage drop in volts

Input guide

1) System type (single-phase or three-phase)

Use single-phase for most small residential loads and three-phase for larger commercial or industrial systems.

2) Copper vs aluminum

Copper has lower resistance and higher ampacity for the same size. Aluminum is lighter and often less expensive, but usually requires a larger cross-section.

3) Current or power input

If you know equipment current, enter amps directly. If you know only kW, the calculator estimates current using system type, voltage, and power factor.

4) Voltage drop target

Common design targets are around 2% to 5% depending on local code, total feeder + branch design, and performance needs.

Quick practical recommendations

• Use a margin (10% to 25%) for future load growth and warmer operating conditions.
• Long cable runs are usually governed by voltage drop before ampacity.
• Motor loads are sensitive to low voltage; tighter drop limits may be beneficial.
• Always verify final design against your local electrical code and installation method tables.

Important engineering note

This tool is intended for preliminary sizing. Real projects should also evaluate ambient temperature correction factors, bundling/derating, insulation type, conduit fill, short-circuit withstand, earth fault loop requirements, and protective device coordination.

For safety-critical or code-regulated installations, final cable selection should be confirmed by a licensed electrician or electrical engineer.