Wire Resistance Calculator
Resistance of a conductor from its length, cross-section and resistivity.
Results
Resistance
0.70000
Ω
Resistance
7.0000
Ω/km
What this tool does
Resistance rises with length and falls with cross-section, which is the whole basis of cable sizing. The default resistivity is the value commonly used for copper at 20 °C; aluminium is about 0.028 Ω·mm²/m, and both rise by roughly 0.4 % per degree of temperature.
Formula
R = ρ × L ÷ S
Variables
| Symbol | Meaning | Unit |
|---|---|---|
l | One-way cable length | m |
s | Conductor cross-section | mm² |
ro | Resistivity | Ω·mm²/m |
R | Resistance | Ω |
Rk | Resistance | Ω/km |
Worked example
- One-way cable length100 m
- Conductor cross-section2.5 mm²
- Resistivity0.0175 Ω·mm²/m
- Resistance0.70000 Ω
- Resistance7.0000 Ω/km
Limitations
- Electrical installations are governed by national wiring rules. Cable sizing also depends on installation method, grouping, ambient temperature and protection devices, which this calculator does not evaluate.
- The calculation runs at full precision and only the display is rounded. If you copy an intermediate value and retype it, small differences can appear.