Wire Resistance Calculator for Copper and Aluminum Cables

R = ρ × L / S

Where：

（1）R = Resistance (Ω)

（2）ρ = Resistivity (Ω* mm² / m)

（3）L = Length (m)

（4）S = Wire size (mm²)

Calculate DC resistance of copper or aluminum wires with temperature correction, parallel conductors, and mm²/AWG input. Supports IEC 60228 & NEC Table 8 for accurate voltage drop and power loss estimation.

Accurately compute the DC resistance (in ohms) of electrical conductors based on material, cross-section, length, temperature, and parallel configuration. Designed for engineers sizing feeders, analyzing losses, or verifying compliance with IEC 60228 and NEC Chapter 9.

Why Resistance Matters in Real Systems

• A 0.1 Ω resistance in a 100 A DC circuit causes 10 V drop and 1 kW of wasted heat

• Aluminum’s higher resistivity requires ~56% larger cross-section than copper for equal performance

• Operating at 75°C vs. 20°C increases copper resistance by over 20%

• Two parallel conductors halve total resistance—but only if perfectly balanced

Core Calculation Method

The tool applies the temperature-corrected resistivity formula:

R = ρ20 · (1 + α · (T - 20)) · L / A · (1 / N)

Where:

• R: Total DC resistance (Ω)

• ρ₂₀: Resistivity at 20°C (Cu: 1.724×10^-8 Ω·m, Al: 2.826×10^-8 Ω·m)

• α: Temperature coefficient (Cu: 0.00393 /°C, Al: 0.00403 /°C)

• T: Conductor operating temperature (°C)

• L: Length in meters

• A: Cross-sectional area in m² (auto-converted from mm² or AWG per IEC 60228)

• N: Number of identical parallel conductors

Note: This calculation assumes uniform current distribution and homogeneous conductor material. Not valid for high-frequency AC.

Material Comparison Example

Scenario: Select conductor for a 150 m, 80 A DC link at 600 V. Max allowable drop: 3% (18 V).

Result: Aluminum achieves comparable performance with proper upsizing—validating cost-effective design.

Key Limitations

• No AC effects: Skin effect, proximity effect, and inductance are ignored

• Uniform temperature assumed: Does not model thermal gradients along the cable

• Ideal parallel balance: Assumes identical impedance in all parallel paths

• Stranding factor not applied: Uses nominal area; real stranded wire may have 1–2% higher resistance

Industry-Specific Applications

For Professionals Who

• Specify conductor materials and sizes to meet voltage drop limits in renewable energy systems

• Quantify I²R losses in DC power distribution for energy efficiency audits

• Verify compliance with NEC Chapter 9 Table 8 or IEC 60228 resistivity requirements

• Design low-voltage control circuits where even 0.5V drop matters

• Teach the relationship between resistivity, temperature, and conductor geometry

Reference Standards

• IEC 60228: Standardizes conductor cross-sections and maximum DC resistance values

• NEC Chapter 9, Table 8: Provides DC resistance data for copper conductors at 75°C

• IEEE 835: Recommended practice for calculating conductor resistance with temperature correction

• BS 6361: British standard for resistivity of copper and aluminum conductors