Voltage Drop Calculator

Unit system

SI (m, mm²)

Imperial (ft, AWG)

Circuit type System voltage (V) Load current (A) One-way run length

Conductor material Conductor size type

Operating temperature (°C) (optional) Target max % drop

Voltage drop: — V

Percent drop: — %

Load-end voltage: — V

Formulas & assumptions

These numbers are indicative only, consult a certified electrician for professional advice.
Resistance at 20 °C: R₂₀ = ρ · L / A, with ρ_Cu = 1.724×10⁻⁸ Ω·m, ρ_Al = 2.826×10⁻⁸ Ω·m.
Temperature adjustment: R_T = R₂₀ · [1 + α (T − 20 °C)], α_Cu ≈ 0.00393/°C, α_Al ≈ 0.00403/°C.
Voltage drop (resistive approximation):
DC & Single-phase: ΔV = 2 · I · L · R_m
Three-phase: ΔV = √3 · I · L · R_m
Percent drop = (ΔV / V_system) × 100. Load-end voltage = V_system − ΔV.
Assumes mostly resistive loads and short residential runs (reactance neglected).
Compliance note: Many wiring codes (e.g., AS/NZS 3000 in AU/NZ) recommend ≤3% drop on final subcircuits. Always check local regulations.

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