Wire Resistance Calculator for Copper and Aluminum Cables

Wire size *

Conductors in parallel *

Length *

Temperature *

Conductor *

Cable type *

Description

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).

Option	Size	Area (mm²)	R (Ω)	V Drop (V)	Verdict
Copper	2 AWG	33.6	0.077	6.16	✅ Acceptable
Aluminum	1/0 AWG	53.5	0.076	6.08	✅ Acceptable, lower cost

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

Field	Use Case	Why It Matters
Solar PV	String-to-combiner wiring	Every 0.5% power loss reduces annual energy yield
Battery Energy Storage	Inter-rack busbars	High pulse currents make low R critical for efficiency
Industrial Control	24VDC sensor loops	Excessive drop causes false signals or relay chatter
EV Charging	DC fast charger cables	I²R heating limits continuous current rating
Audio Engineering	Speaker wire runs	Resistance affects damping factor and bass response

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

Frequently Asked Questions

How does temperature affect wire resistance?

Resistance increases linearly with temperature. For every 10°C rise, copper resistance increases by ~4%. Always use operating temperature—not ambient—for accurate calculations.

Why is my calculated resistance different from the cable datasheet?

Datasheets list maximum DC resistance at 20°C. This calculator computes actual resistance at your specified temperature and length, including parallel conductors—providing a more realistic value for design.

Can I use this for AC circuits?

Only for rough estimates. AC resistance includes skin effect and proximity effects. Use an AC impedance calculator for final design.

Does AWG to mm² conversion affect accuracy?

Yes—this tool uses standard cross-sectional areas from IEC 60228 (e.g., 10 AWG = 5.26 mm²), not nominal values. This ensures compliance with international standards.

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