Work out wire size for current instantly with clear inputs, formula shown and shareable results.
Sizing for voltage drop rearranges Ohm's law: required area equals 2 x resistivity x length x current divided by the permitted drop in volts. Copper resistivity is about 0.0172 ohm mm2/m at 20 C. The result must then be checked against the ampacity table for the installation method.
Cable sizing
A = 2 x rho x L x I / Vdrop_allowed; then verify ampacity for the installation method
Electrical results are planning estimates only. Verify against the applicable wiring rules (IEC 60364, BS 7671, NEC or local code) and have all installation work designed and checked by a qualified electrician.
On long runs voltage drop dominates; on short runs ampacity does. Both must be satisfied, and the larger result governs.
For accuracy yes — copper resistivity rises about 0.4% per degree, so a conductor at 70 C is roughly 20% more resistive than at 20 C.