Electrical
Voltage Drop Calculator
Estimate copper wire voltage drop in V for single-phase or balanced three-phase circuits using built-in mm² and AWG resistance tables at 20°C.
How it works
Vd(single) = 2 × L × I × R / 1000; Vd(three) = √3 × L × I × R / 1000
For 2.5 mm² copper (R = 7.41 Ω/km), a 30 m one-way run at 10 A in a single-phase circuit gives Vd = 2 × 30 × 10 × 7.41 / 1000 = 4.45 V (rounded).
L is one-way length in m, I is line current in A, and R is conductor resistance in Ω/km. This resistive estimate assumes unity power factor and excludes cable reactance. The three-phase result is line-to-line drop. Resistance data: Nexans Power Cable Catalogue 2019, Table 2.4 (metric plain copper); Genesis Product Catalog 2023, page 66 (AWG solid copper).
FAQ
Should I enter the return cable length too?
No. Enter only the one-way distance from source to load. The single-phase or two-wire DC formula already accounts for the return conductor.
Do AWG and mm² sizes represent identical wires?
No. Select the actual size system. Each option displays its built-in DC resistance in Ω/km at 20°C.
Does this include hot cable resistance or cable sizing rules?
No. Resistance rises with conductor temperature. This estimate excludes temperature correction, reactance, and installation-specific current capacity.