Voltage Drop Calculator

Calculate the voltage lost to resistance over a wire run. Exceeding a 3% drop for branch circuits or 5% for feeder circuits is generally a violation of NEC recommendations.

Manual Formula (No-JS Fallback)

Vd = (2 * K * I * L) / CM

• K: Direct current constant (12.9 ohms/cmil-ft for Copper)
• I: Current in Amperes
• L: One-way length in feet
• CM: Circular Mils of the wire

Assumptions: 100% duty cycle, DC or single-phase AC, ignoring reactance.