Calculator KB-47
Wire Resistance Calculator
From windings and extension cords to DIY shunts and heating elements.
Result
In brief: Calculate wire resistance by length and diameter or cross-sectional area for different metals, with temperature correction. Compare materials on one graph. Example: Resistance: 2.228 Ω.
Calculation example
| Material | Copper |
|---|---|
| Length | 100 м |
| Temperature | 20 °C |
| Known values | Diameter, mm |
| Value | 1 |
| Resistance | 2.228 Ω |
|---|---|
| Per meter | 22.28 mΩ/m |
| Wire gauge | 0.785 mm² |
| Diameter | 1 mm |
| At 20 °C | 2.228 Ω |
How it is calculated
RT = R₂₀ · (1 + α · (T − 20))
Resistance is proportional to length and inversely proportional to cross-sectional area. It increases noticeably with heat for copper and aluminum, by about 0.4% per degree, but barely changes for manganin and constantan.
What to look for
- Cheap copper-clad aluminum (CCA) wire has resistance closer to aluminum than to copper.
- Measure low resistances using a four-wire method: multimeter probes add their own tenths of an ohm.
Frequently asked questions
What is the resistance of 100 m of copper wire with a diameter of 1 mm?
The cross-sectional area is 0.785 mm², so R = 0.0175 · 100 / 0.785 ≈ 2.23 Ω at 20 °C.
How does wire resistance depend on temperature?
For copper and aluminum, it increases by about 0.39% per degree: heating from 20 to 70 °C raises it by almost 20%. For manganin and constantan, it barely changes.
How do you determine the length of wire on a spool from its resistance?
L = R · S / ρ. A copper wire with a diameter of 1 mm and a resistance of 2.23 Ω is about 100 m long. Measure low resistances using a four-wire method.
