Wire Resistance Calculator — R = ρL/A with Temperature
Find the DC resistance of any wire or conductor — choose the material, enter the length and diameter, adjust the temperature and get the resistance in ohms with conductance and resistance per metre.
Conductor material
m
mm
°C
DC resistance at the specified temperature
- 1
Cross-section area: π × (d ÷ 2)²
π × (2 mm ÷ 2)² = 3.142 mm² - 2
Temperature-corrected resistivity: ρ₀ × (1 + α × ΔT)
1.68 × (1 + 0.00393 × (20 − 20)) × 10⁻⁸ = 1.68 × 10⁻⁸ Ω·mα is the temperature coefficient of resistance for copper. - 3
Resistance: ρ × L ÷ A
1.68 × 10⁻⁸ × 10 m ÷ (3.142 × 10⁻⁶ m²) = 0.0535
How does this calculator work?
Wire resistance R = ρ L / A, where ρ is resistivity (e.g. copper 1.68 × 10⁻⁸ Ω·m), L is length in metres, A = π(d/2)² from diameter in mm. Temperature correction: ρ(T) = ρ₀[1 + α(T − 20)]. Select material, enter length, diameter and temperature to get DC resistance and conductance.
Formula
How this is calculated
The resistance of a uniform conductor is R = ρ L / A, where ρ is the material's resistivity (Ω·m), L is the length (m) and A is the cross-section area (m²). Resistivity is an intrinsic property that quantifies how strongly a material opposes current flow; smaller ρ means a better conductor. Silver is the best common conductor (ρ ≈ 1.59 × 10⁻⁸ Ω·m), followed closely by copper (1.68 × 10⁻⁸), while nichrome is roughly 65 times more resistive than copper, which is why it is used in heating elements.
Resistance increases with temperature for metals. The temperature coefficient of resistance α gives the fractional change per degree Celsius: ρ(T) = ρ₀ × [1 + α(T − 20)], where 20 °C is the standard reference temperature. Copper's α ≈ 0.00393 /°C means its resistance rises by about 0.4% per degree — a wire at 80 °C has roughly 23% higher resistance than at 20 °C. This matters for motor windings, long power cables and precision measurement circuits.
This calculator gives DC resistance only. At high frequencies the skin effect confines current to the conductor surface, increasing effective resistance beyond the DC value. In AC power systems, the AC resistance of large conductors can be 5–10% higher than their DC resistance. The results here assume uniform circular cross-section and pure conductor material at the stated temperature.
Frequently asked questions
The International Annealed Copper Standard (IACS) gives copper resistivity as 1.7241 × 10⁻⁸ Ω·m at 20 °C. This calculator uses 1.68 × 10⁻⁸ Ω·m, the standard textbook and NBS value. The difference is less than 3% and reflects the purity and annealing state of the copper.
For metals, resistance increases linearly with temperature: R(T) = R₀[1 + α(T − 20)]. Copper's α ≈ 0.00393/°C, so at 100 °C (e.g. a heavily loaded cable), its resistance is about 31% higher than at room temperature. Nichrome has α ≈ 0.0004/°C and is therefore used where stable resistance across a wide temperature range matters (heating elements, precision resistors).
A larger cross-section provides more parallel paths for electrons, reducing resistance — exactly as adding parallel resistors reduces total resistance. Doubling the diameter quadruples the area, cutting resistance to one-quarter. This is why high-current cables use thick conductors even though the resistivity of the metal itself is unchanged.
Also known as
TG we-Calculate Editorial Team. (2026). Wire Resistance Calculator — R = ρL/A with Temperature [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/wire-resistance-calculator
TG we-Calculate Editorial Team. "Wire Resistance Calculator — R = ρL/A with Temperature." TG we-Calculate. 2026. https://we-calculate.com/calculator/wire-resistance-calculator.
TG we-Calculate Editorial Team, "Wire Resistance Calculator — R = ρL/A with Temperature," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/wire-resistance-calculator
@misc{wecalculate_wire_resistance_calculator, title = {Wire Resistance Calculator — R = ρL/A with Temperature}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/wire-resistance-calculator}}, year = {2026}, note = {TG we-Calculate} }
Did this calculator help you?