Cable Resistance Calculator
Calculate conductor resistance from material, length and cross-sectional area.
About Cable Resistance Calculator
Resistance rises with length and falls with area. Copper resistance increases about 0.39 per cent per kelvin, so a conductor at its 70 °C rating has roughly 20 per cent more resistance than at 20 °C — which matters for both voltage drop and fault calculations. Loop resistance is twice the one-way value because current must return, and it is the loop figure that determines voltage drop and earth fault current.
Formula
Cable Resistance
R = ρ L ÷ A, with ρ corrected for temperature as ρ₂₀(1 + α ΔT)
- ρ
- Resistivity of the conductor material
- α
- Temperature coefficient of resistance
Worked example
With the default values below, Cable Resistance Calculator returns Loop Resistance of 0.34379. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Cable length one wayminimum 0 m
- 50 m
- Conductor cross-sectional areaminimum 0.01 mm2
- 6 mm2
- Conductor materialone of Copper, Aluminium
- Copper
- Conductor temperatureaccepts -50–250 C
- 70 C
Results
- Loop Resistance
- 0.34379 ohm
- One-Way Resistance
- 0.17190 ohm
- Resistivity at That Temperature
- 0.0000000206 ohm m
- Resistance per Kilometre
- 3.4379 ohm
- Resistance at 20 Degrees
- 0.14367 ohm
Step by step
- 1Values used
- 2Cable Resistance
- 3Loop Resistance= 0.34379 ohm
- 4One-Way Resistance= 0.17190 ohm
- 5Resistivity at That Temperature= 0.0000000206 ohm m
- 6Resistance per Kilometre= 3.4379 ohm
- 7Resistance at 20 Degrees= 0.14367 ohm
Assumptions and limits
- The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to 10 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
How is Cable Resistance calculated?
R = ρ L ÷ A, with ρ corrected for temperature as ρ₂₀(1 + α ΔT) Resistance rises with length and falls with area. Copper resistance increases about 0.39 per cent per kelvin, so a conductor at its 70 °C rating has roughly 20 per cent more resistance than at 20 °C — which matters for both voltage drop and fault calculations.
Why does Cable Resistance matter?
Loop resistance is twice the one-way value because current must return, and it is the loop figure that determines voltage drop and earth fault current.
What values do I need to enter?
This calculator takes 4 inputs: Cable length one way, Conductor cross-sectional area, Conductor material, Conductor temperature. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.