Voltage Drop Calculator
Calculate voltage drop, percent drop and final load voltage for DC, single-phase and three-phase circuits
Calculator
Select your system type and input method to compute voltage drop, percentage voltage drop, and load voltage for cables based on current, length, and either cable resistance or conductor material & size.
About the Voltage Drop Calculator
The Voltage Drop Calculator helps you quickly estimate voltage drop, percentage voltage drop, and final load voltage in DC, single-phase AC, and three-phase AC circuits. You can calculate using either cable resistance per unit length or conductor material and cross-sectional area, making this tool ideal for electrical designers, installers, and engineering students.
What You Can Calculate
- Voltage Drop (ΔV): The difference between source voltage and voltage at the load terminals.
- Percent Voltage Drop (%ΔV): Voltage drop as a percentage of the supply voltage, useful for checking compliance with design limits.
- Load Voltage (Vload): The actual voltage available at the load after accounting for cable losses.
- Cable Resistance (R): Effective loop resistance of the circuit based on length and conductor properties.
Formulas Used in the Calculator
The calculator uses standard electrical engineering relationships for voltage drop in cables. First, the conductor resistance is found from either resistance per unit length or from material resistivity:
- From resistance per unit length: Rcond = rL × L
- From resistivity and area: Rcond = ρ × (L / A)
where rL is the resistance per unit length, L is the one-way cable length, ρ is the conductor resistivity, and A is the conductor cross-sectional area.
The voltage drop for each system type is then calculated as:
- DC & Single-Phase AC: ΔV = 2 × I × Rcond
- Three-Phase AC (balanced): ΔV = √3 × I × Rcond
The corresponding load voltage and percentage voltage drop are:
- Load Voltage: Vload = Vsource − ΔV
- Percent Drop: %ΔV = (ΔV / Vsource) × 100
How to Use the Calculator
- Select the system type (DC, single-phase AC, or three-phase AC).
- Enter the supply voltage, load current, and cable length with your preferred units.
- Choose a calculation method:
- Resistance per length: Enter cable resistance in Ω/m, Ω/km, Ω/ft, Ω/1000 ft, or total Ω.
- Material & area: Select conductor material (copper or aluminum) and input cross-sectional area.
- The calculator automatically computes voltage drop, percent drop, and load voltage.
Applications of Voltage Drop Calculation
Voltage drop calculations are essential for cable sizing, power distribution design, and system efficiency analysis. Excessive voltage drop can lead to equipment malfunction, reduced motor torque, overheating, and energy losses. This calculator helps engineers, electricians, and system designers verify that cables are adequately sized, comply with design standards, and deliver sufficient voltage to sensitive loads over long runs.