Long, thin wires have more resistance, which wastes power as heat and lowers the voltage at the load.
How to use the Wire Resistance Calculator
- Material
- Wire length
- Cross-section
- Current
Results update as you type, and every field accepts the units shown in its menu.
How it works
Multiply the material’s resistivity by length and divide by the cross-sectional area.
Inputs explained
| Field | What to enter |
|---|---|
| Material | Choose one: Copper (1.68×10⁻⁸ Ω·m), Aluminium (2.65×10⁻⁸), Silver (1.59×10⁻⁸), Gold (2.44×10⁻⁸) … |
| Wire length | Units: m, cm, mm, km, in, ft … |
| Cross-section | Units: mm², m² |
| Current | Units: A, mA, µA |
What each result means
- Resistance = [Material] × [Wire length] ÷ [Cross-section]
- Voltage drop = [Resistance] × [Current]
- Power lost as heat = [Current]^2 × [Resistance]
Example values
How the main result changes when Wire length changes and everything else stays at the example values above:
| Wire length (m) | Resistance (Ω) |
|---|---|
| 10 | 0.0672 |
| 15 | 0.1008 |
| 20 | 0.1344 |
| 25 | 0.168 |
| 30 | 0.2016 |
| 40 | 0.2688 |
Formula
R = ρ × L ÷ AWorked example
Inputs — Material: Copper (1.68×10⁻⁸ Ω·m); Wire length: 20 m; Cross-section: 2.5 mm²; Current: 10 A.
Results — Resistance = 0.1344 Ω; Voltage drop = 1.344 V; Power lost as heat = 13.44 W.
Frequently asked questions
Does this include both conductors?
No; for a round trip, double the length.
Does temperature change resistance?
Yes, copper’s resistance rises about 0.4% per °C.
What formula does the Wire Resistance Calculator use?
R = ρ × L ÷ A.