Should voltage drop cable length be one way?

Yes. Enter one-way source-to-load length; the DC and single-phase formulas include the return conductor.

Does a voltage drop calculator replace an ampacity check?

No. Ampacity, insulation, terminals, protection and installation conditions must be checked separately.

Voltage Drop Calculator: DC, Single & Three Phase

DC, single-phase and three-phase conductor analysis

Analyze Voltage Loss from Source to Load

Calculate volts lost, percent drop, load voltage, conductor loss and a larger size that meets your selected limit. Current can be entered directly or derived from watts, kilowatts or horsepower.

Calculation task

Choose the electrical calculation

Circuit and load

Circuit type

Source voltage (V)Load entry methodLoad current (A)

Conductor run

One-way lengthLength unitConductor materialConductor size systemConductor sizeParallel conductors per phase / polarityConductor temperature (°C)

Advanced impedance and limit

Maximum desired drop (%)Operating hours per yearElectricity price per kWh

Source-to-load visual

Important: this is a voltage-drop and conductor-loss estimate. It does not determine ampacity, insulation rating, terminal temperature, fault protection, installation method or electrical-code compliance.

Electrical results

Resistance voltage drop calculator and Ohm’s law

Direct mode solves one missing electrical quantity from measured or specified values: resistance equals voltage divided by current, voltage equals current multiplied by resistance, current equals voltage divided by resistance, and power equals voltage multiplied by current. This component-level mode is separate from the conductor model below.

Voltage drop formulas

For a DC or single-phase resistive circuit, the round-trip conductor length gives Vdrop = 2IRL. For a balanced three-phase circuit, Vdrop = √3IRL. In advanced AC mode, the calculator uses the entered power factor and reactance in the approximate expression R cosφ + X sinφ.

Temperature and parallel conductors

Metal resistance rises with conductor temperature. This tool adjusts resistivity from 20°C using a material temperature coefficient. Parallel conductors divide the effective resistance and reactance by the number entered.

Interpreting 3% and 5%

Three percent and five percent are common design reference values, but requirements depend on equipment, circuit type and governing rules. The selected limit is a user-controlled design target, not an automatic compliance decision.

Voltage drop questions

Is cable length one way or round trip?

Enter one-way source-to-load length. The DC and single-phase formulas apply the return path automatically.

Can this recommend a wire size?

It reports the smallest listed size meeting the selected voltage-drop limit. You must still verify ampacity and installation requirements separately.

Why can AC results differ from simple DC resistance?

Power factor and conductor reactance can contribute to AC voltage drop, particularly on larger or longer circuits.

Voltage Drop Calculator