Wire Length from Resistance Calculator

About this calculator

A wire's resistance depends on its material, length, and cross-sectional area through R = ρL/A, where ρ is the material's resistivity, L is length, and A is cross-sectional area. Solving for length gives L = R·A/ρ — the length of wire needed to hit a target resistance for a chosen diameter and material. Copper (ρ ≈ 1.68×10⁻⁸ Ω·m) and aluminum (ρ ≈ 2.65×10⁻⁸ Ω·m) are the most common conductors and differ noticeably in how much wire it takes to reach the same resistance.

Electricians and electrical engineers use this to size wire runs and check voltage drop over distance, while hobbyists use it for projects like winding transformer or inductor coils, building heating elements, or choosing speaker wire gauge for long cable runs.