Wire Resistance Calculator
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Other tools you may find usefulCable resistance calculator - calculate the electrical resistance of a cable online
Check the electrical resistance of the cable depending on its length, cross-section, material and operating temperature. The cable resistance calculator allows you to quickly determine voltage drop, power loss and connection efficiency in low- and high-voltage installations. An ideal tool for electricians, designers, automation engineers and electrical engineering students.
Run the cable calculator See formulas and examples
What does the wire resistance calculator calculate
- The resistance of a wiredepending on the length, cross-section and material.
- Voltage dropon the wire at a given current and rated voltage.
- Power lossin power or signal cables.
- Temperature correctionresistivity for copper, aluminum and other materials.
- Effective resistancefor two-wire connections (current loop).
Formula for cable resistance
where: R – resistance [Ω], ρ – specific resistance [Ω·mm²/m], L – cable length [m], A – cross-section [mm²].
Temperature correction of resistivity
where: ρ₀ – resistivity at reference temperature (e.g. 20°C), α – temperature coefficient, T – operating temperature.
Specific resistivity of selected materials (at 20°C)
| Material | Specific resistivity ρ [Ω·mm²/m] | Coefficient α [1/°C] | Notes |
|---|---|---|---|
| Copper (Cu) | 0.0172 | 0.00393 | The best conductor for general use |
| Aluminum (Al) | 0.0282 | 0.00403 | Light, cheaper, higher losses |
| Silver (Ag) | 0.0168 | 0.00380 | Best electrical conductor |
| Iron (Fe) | 0.10 | 0.00651 | Used in heating elements |
| Nickel (Ni) | 0.07 | 0.00600 | Corrosion resistant |
Calculation examples
Copper wire 2.5 mm²
Length 30 m, ρ = 0.0172 Ω mm²/m:
R = 0.0172 × (30 / 2.5) = 0.206 Ω
Voltage drop at 10 A: U = I × R = 10 × 0.206 = 2.06 V
Aluminum wire 6 mm²
Length 40 m, ρ = 0.0282 Ω mm²/m:
R = 0.0282 × (40 / 6) = 0.188 Ω
Voltage drop at 15 A: U = 15 × 0.188 = 2.82 V
Voltage drop - formula and interpretation
Voltage drop [V] = current [A] × cable resistance [Ω]
Selection of the cable cross-section
- Determine the permissible voltage drop (e.g. 3% for a 230 V installation).
- Calculate the length of the circuit including current return (loop).
- Select the cross-section so that the decline does not exceed the permissible value.
- Take into account the material and temperature - the warmer, the greater the resistance.
- For currents >50 A or lengths >50 m, consider aluminum or copper cables with a larger cross-section.
Practical applications of the calculator
Home installations
Calculate voltage drops for lighting, sockets or pumps. Ensure compliance with PN-HD 60364.
Industry and automation
Check the length of signal cables in control systems, avoiding interference.
Photovoltaics and energy storage
Minimize power loss and excessive heating in the DC cables between modules and the inverter.
Low-voltage systems (LED, CCTV, alarms)
Select the cross-section to avoid voltage drops in long low-voltage lines.
FAQ
Why does resistance depend on length?
The longer the wire, the greater the resistance to the flowing current - proportional to the length L.
Does the material matter?
Yes. Copper conducts approximately 40% better than aluminum, which allows the use of thinner wires.
How to take temperature into account?
Use the temperature coefficient α – for copper 0.00393/°C. Resistance increases with temperature.
How to calculate loop resistance?
Multiply the result by 2 - current flows back and forth through the wire.
Summary:The wire resistance calculator allows quick calculations for copper, aluminum and other materials. It facilitates the selection of cross-section, minimizes voltage drops and helps in the design of safe, energy-efficient installations.