Voltage Drop & Wire Size Calculator

All table values are based on NFPA 70, NEC 2014.

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Wire Material (K)

    • Ω*cmil/ft
    • Ω*cmil/m

Load (I)

Load Factor

Length One-way (L)

Ambient Temperature

Voltage Drop Percentage


Wire Circular Mil Area (ACM)

Voltage Drop Formulas

Voltage Drop (V)\begin{align}\frac{2KIL}{A_{CM}}\end{align}\begin{align}\frac{\sqrt{3}KIL}{A_{CM}}\end{align}
Circular mil area (ACM)\begin{align}\frac{2KIL}{VoltageDrop}\end{align}\begin{align}\frac{\sqrt{3}KIL}{VoltageDrop}\end{align}
Resistance change due to temperature relative to 75℃\begin{align}R_2 &=R_1[1 + \alpha(T_2 - 75)]\\\alpha_{cu}&=0.00323\\\alpha_{al}&=0.00330\end{align}

Visit https://www.mikeholt.com/technnical-voltage-drop-calculations-part-two.php for a detailed explanation of voltage drop calculations.