Wire Resistance Calculator
How much resistance does a length of wire add to your circuit?
Your numbers
Your results
Resistance (Ω)
Resistance (Ω)
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Resistance per 100 m (Ω)
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Cross-section (mm²)
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Wire Resistance Calculator by TheCalcTools
How the Wire Resistance Calculator works
Choose the conductor material and enter its length and diameter.
The cross-sectional area comes from the diameter.
Resistance is resistivity × length ÷ area at about 20°C.
The formula
R = ρ × L ÷ AA = π × (d ÷ 2)²
Worked example
Using the default values shown in the calculator:
| Material | Copper (1.68 × 10⁻⁸ Ω·m) |
|---|---|
| Length (m) | 50 |
| Diameter (mm) | 1.5 |
- Area = π × 0.75² = 1.767 mm².
- R = 1.68×10⁻⁸ × 50 ÷ area = 0.4753 Ω.
Result:
| Resistance (Ω) | 0.4753 |
|---|---|
| Resistance per 100 m (Ω) | 0.9507 |
| Cross-section (mm²) | 1.767 |
Frequently asked questions
Does temperature change the result?
Yes. Copper’s resistance rises about 0.39% per °C. The values here are at 20°C.
Why does thickness matter so much?
Resistance falls with the square of the diameter, so doubling the diameter cuts resistance to a quarter.
Sources and further reading
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This calculator gives estimates for information only. Check important results independently before you rely on them. See our disclaimer.