# Wire Resistance Calculator

URL: https://speedycalculator.com/calculators/physics/wire-resistance/
Last updated: 2026-10-25

> The wire resistance calculator finds the resistance of a wire from its material, length and cross-sectional area, R = ρL ÷ A, and the voltage drop at a given current.

## Inputs

- Material
- Wire length (m, cm, mm, km, in, ft, yd, mi)
- Cross-section (mm², m²)
- Current (A, mA, µA)

## Results

- Resistance
- Voltage drop
- Power lost as heat

## Formula

```
R = ρ × L ÷ A
```

## Explanation

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

FieldWhat to enterMaterialChoose one: Copper (1.68×10⁻⁸ Ω·m), Aluminium (2.65×10⁻⁸), Silver (1.59×10⁻⁸), Gold (2.44×10⁻⁸) …Wire lengthUnits: m, cm, mm, km, in, ft …Cross-sectionUnits: mm², m²CurrentUnits: 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)100.0672150.1008200.1344250.168300.2016400.2688

## Worked 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.

## FAQ

**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.