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12V DC Voltage Drop Calculator

Calculate voltage drop in 12 volt DC systems.

System voltage12 V DC
From power source to equipment. Return cable is included automatically.

The calculation includes an equal-length separate return cable. Chassis/frame returns are not included.

Voltage drop0.00 V(0.0 %)
Voltage at equipment12.00 V
Resistance (total)0.000 Ω

How the calculation works

Enter the cable length one way. The calculator includes an equal-length separate return cable, then calculates resistance from the total cable length and cable area.

R = ρ × L_total ÷ A
  • ρ (rho) — copper resistivity, approximately 0.0175 Ω·mm²/m at 20 °C.
  • L_total — entered one-way cable length × 2, in metres.
  • A — cable cross-section in mm².

Voltage drop, percentage and voltage at equipment are then found from:

V_drop = I × R
V_drop % = (V_drop ÷ 12) × 100
V_load = 12 − V_drop

Return cable

This standard calculation assumes separate positive and negative cables of equal length. Chassis/frame returns are not included and should be assessed separately.

Notes and limitations

This calculator uses copper cable values at 20 °C. For critical or safety-related work, check cable manufacturer data and relevant electrical standards.