voltage drop calculator in DC or AC circuit

This value only used for adjusting conductor resistance.

Length of cable in feet (one-way distance)

  Load current in amperes


Estimated voltage drop

Select the material either copper or aluminum, the size of the conductor, the voltage and phase from a list of common voltages, then enter the one way circuit length in feet, and load in amperes..

Online voltage drop calculator in DC or AC circuit:

Use this calculator to estimate cable voltage drop for sizing conductors.

Table of contents:

What is voltage drop?

Voltage drop is the decrease of electrical potential along the path of a current flowing in an electrical circuit. Voltage drops in the internal resistance of the source, across conductors, across contacts, and across connectors are undesirable because some of the energy supplied is dissipated. The voltage drop across the electrical load is proportional to the power available to be converted in that load to some other useful form of energy. For example, an electric space heater may have a resistance of ten ohms, and the wires that supply it may have a resistance of 0.2 ohms, about 2% of the total circuit resistance. This means that approximately 2% of the supplied voltage is lost in the wire itself. An excessive voltage drop may result in the unsatisfactory performance of a space heater and overheating of the wires and connections.

How do you calculate voltage drop?

The table below gives the usual formulas which make it possible to calculate the voltage drop in a given circuit per km of length.

IB: operating current in amperes

L: cable length in km

R: linear resistance of a conductor in Ω / km

S: Cross sectional area of copper in mm2

R=23.7/S for copper

R=37.6/S for aluminum

Note: R is negligible beyond a section of 500 mm2

linear reactance of a conductor in Ω / km; X is negligible for cables with a cross section of less than 50 mm2.

In the absence of other indication, X = 0.08 Ω / km will be taken.

φ: phase shift of the current on the voltage in the circuit considered; usually:

lighting: cos φ = 1

driving force: when starting: cos φ = 0.35, in normal service: cos φ = 0.8.

Un: nominal voltage between phases

Vn: nominal voltage between phase and neutral

For prefabricated pipes, resistance R and reactance X are indicated by the manufacturer.

Voltage drop calculation formulas

Circuit Voltage drop(ΔU)
in volts in %
Two phases ΔU=2IB(R cosφ+X sinφ)L


Phase and neutral ΔU=2IB(R cosφ+X sinφ)L (100ΔU)/Vn
Three phases ΔU=√3IB(R cosφ+X sinφ)L (100ΔU)/Un