Wire Resistance Calculator

Wire Resistance Calculator. Enter your wire material, length, diameter, and operating temperature to calculate wire resistance, conductance, voltage drop, and power loss. The Wire Resistance Calculator applies Pouillet's Law (R = ρ × L / A) with temperature correction, giving you results for copper, aluminum, silver, gold, tungsten, and more. Also try the Delta to Wye Conversion Calculator.

Results

Resistance at Operating Temp

Resistance at 20°C

Cross-Section Area

Conductance

Voltage Drop

Power Loss

Resistance per Meter

How do I calculate the resistance of a wire?

Wire resistance is calculated using Pouillet's Law: R = ρ × L / A, where ρ is the material's resistivity (in Ω·m), L is the wire length (in meters), and A is the cross-sectional area (in m²). For a round wire, A = π × (d/2)², where d is the diameter. This calculator handles all that math automatically once you enter your inputs. See also our Wire Size Calculator.

How does wire length affect resistance?

Resistance is directly proportional to wire length — doubling the length doubles the resistance. This is because a longer wire presents more collisions between electrons and the conductor's atoms, impeding current flow more. In practical wiring, keeping runs short reduces voltage drop and power loss.

How does the cross-sectional area of a wire affect resistance?

Resistance is inversely proportional to cross-sectional area. A thicker wire (larger area) has lower resistance because more electrons can flow in parallel. Halving the area doubles the resistance. This is why high-current applications require thicker gauge wires.

What are the four main factors affecting wire resistance?

The four factors are: (1) Material — each conductor has a unique resistivity ρ; (2) Length — longer wire = higher resistance; (3) Cross-sectional area — thicker wire = lower resistance; and (4) Temperature — most metals increase in resistivity as temperature rises, described by R(T) = R₂₀ × [1 + α × (T − 20)].

What is resistivity and how is it different from resistance?

Resistivity (ρ) is an intrinsic material property measured in Ω·m that describes how strongly a material opposes electric current flow, regardless of shape or size. Resistance (R) is the actual opposition of a specific wire and depends on resistivity, length, and area. Think of resistivity as a material constant and resistance as the real-world result.

Why does temperature affect wire resistance?

As temperature increases, atoms in the metal vibrate more intensely, causing more collisions with charge-carrying electrons and increasing resistivity. The relationship is approximately linear: R(T) = R₂₀ × [1 + α × (T − 20°C)]. Copper, for example, has α ≈ 0.00393 /°C, meaning each degree of temperature rise increases resistance by about 0.393%.

What is the resistivity and conductivity of copper?

Copper has a resistivity of approximately 1.68×10⁻⁸ Ω·m at 20°C, making it one of the best electrical conductors available. Its electrical conductivity (σ = 1/ρ) is about 5.96×10⁷ S/m. Annealed copper is slightly less conductive (ρ ≈ 1.72×10⁻⁸ Ω·m) due to its softer, more disordered crystal structure.

What is conductance and how does it relate to resistance?

Conductance (G) is the reciprocal of resistance: G = 1/R, measured in Siemens (S). While resistance measures how strongly a wire opposes current, conductance measures how easily it allows current to flow. A wire with a resistance of 0.01 Ω has a conductance of 100 S. The conductance formula in terms of geometry is G = σ × A / L, where σ is electrical conductivity. You might also find our Power Dissipation Calculator useful.