Cable Resistance Calculator

This tool calculates the DC resistance of a cable based on length, cross-sectional area, conductor material, and temperature. It also computes voltage drop under load (V = I × R) and displays resistivity-adjusted values for copper or aluminum at the specified temperature.

Excessive voltage drop reduces system efficiency, causes equipment malfunction (e.g., dim lights, motor torque loss), and may violate electrical codes (e.g., ≤3% for branch circuits, ≤5% for feeders). This calculator helps ensure compliance and performance across automotive, solar PV, and industrial installations.

“1” selects copper (resistivity ρ₀ = 1.68×10⁻⁸ Ω·m at 20°C); “2” selects aluminum (ρ₀ = 2.82×10⁻⁸ Ω·m at 20°C). The calculator automatically adjusts resistivity for the entered temperature using the linear temperature coefficient (α_Cu = 0.00393/°C, α_Al = 0.00403/°C).

Automotive wiring: 0.5–6 mm²; residential lighting: 1.5–2.5 mm²; solar DC strings: 4–10 mm²; industrial power distribution: 16–95 mm². Always verify against local standards (e.g., NEC Table 310.16, IEC 60364-5-52) and derating factors.

Conductor resistance increases with temperature. The calculator uses R = R₀[1 + α(T − T₀)] to scale resistivity, where T₀ = 20°C. For high-temperature environments (e.g., engine bays or rooftop solar), accurate ambient temp input is critical for realistic voltage drop estimates.

It calculates DC resistance only. For AC applications above ~1 kHz or large conductors (>6 mm²), skin effect and proximity effect increase effective resistance — use specialized AC impedance calculators or consult IEC 60287 for precision. At 50/60 Hz and typical low-voltage cables, DC resistance is a valid approximation.

Increase the cable cross-sectional area or reduce length — both lower resistance proportionally. Doubling CSA halves resistance; halving length also halves resistance. Verify thermal rating (ampacity) isn’t exceeded when upsizing, especially in bundled or high-temp environments.

The calculator assumes ideal geometry and uses nominal CSA. Stranded wire has ~1–3% higher effective resistance due to lay-length and surface roughness. For critical designs, apply a 1.02–1.03 multiplication factor to the result or consult manufacturer datasheets for exact AC/DC resistance values.

No — it models only the conductor’s intrinsic resistance. Real-world installations add contact resistance at lugs, crimps, and breakers (typically 0.1–5 mΩ per connection). Include these in worst-case voltage drop analysis, especially for high-current or safety-critical systems like battery interconnects.

The calculator outputs resistance for *one* conductor. For voltage drop in a complete circuit (e.g., 12 V DC supply to load and back), double the result — because current flows through both the supply *and* return path. Always use loop length (2 × one-way distance) for accurate system-level voltage drop.