Voltage Drop Calculator

Voltage drop and cable loss for a DC string or an AC run, from conductor resistance, length and current.

Design aid, not a substitute for the code, the equipment manual or your AHJ. It uses resistance only, so AC results ignore reactance and power factor. Copper figures are NEC Chapter 9 Table 8 (AWG, 75°C) from a sample whose coated or uncoated column is not labelled (uncoated is about 2% lower), or one maker's datasheet (mm², 20°C). Aluminium is an estimate and may understate Table 8 aluminium by about 1%.
Examples:

Formulas: DC and single-phase AC, drop = 2 × I × R × L. Three-phase, drop = 1.732 × I × R × L. R is resistance per unit length at the conductor temperature, L the one-way length. Resistance changes with temperature as R × (1 + a × (T − Tref)). Table 8 note 2 gives a = 0.00323 (copper) and 0.00333 (aluminium) at 75°C; for the 20°C datasheet sizes this tool uses 0.00393 (copper) and 0.00429 (aluminium). Aluminium resistance is copper × 1.64, between the resistivity ratio (1.58) and the Table 8 aluminium column as printed by OpenExamPrep (about 1.65).