Wire size calculator
Find the minimum copper conductor cross-section that keeps the voltage drop within your limit.
How it is calculated
Allowed drop ΔV = V × (max % ÷ 100). Minimum area A = k × ρ × I × L ÷ ΔV, with k = 2 (single-phase) or √3 (three-phase) and ρ = 0.01724 Ω·mm²/m.
Worked example
Three-phase, 50 A, 100 m, 400 V, 3 % limit: ΔV = 12 V, A = 1.732 × 0.01724 × 50 × 100 ÷ 12 = 12.44 mm². Pick the next standard size, 16 mm².
Steps
- Select the circuit type.
- Enter the load current, one-way length and supply voltage.
- Enter the maximum drop you accept, then choose the next standard conductor size up.
Frequently asked questions
Which size should I buy?
Round up to the next standard size, such as 2.5, 4, 6, 10, 16 mm² (or the AWG equivalent).
Does this size for current carrying capacity too?
No. Also check the ampacity for the installation method and insulation. The larger of the two sizes governs.
Why is the length one-way?
The formula already includes the return path through the factor k.
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References
Copper resistivity and voltage drop relations as in the voltage drop calculator; standard conductor sizes from IEC 60228. Confirm ampacity with the local code.
Estimates for information only. Verify critical values with a qualified engineer or your supplier standards.