Enter any two values (voltage, power, or current) into the calculator to determine the missing value. Use the Three-Phase AC tab for balanced three-phase calculations with power factor.

Amp Drop Calculator

Use the main tab for real conductor voltage drop. Keep the power and current solver as a secondary utility.

Voltage Drop Inputs

Enter current, source voltage, one-way run length, conductor material, and wire size.

120 V
208 V
240 V
277 V
480 V

P-V-I Solver

Enter any 2 values to calculate the missing one for resistive or DC loads.

Three-Phase AC Solver

Enter any 3 values to calculate the missing one for a balanced load.

Results

    Amp Drop Formula

    The following formulas are used by this calculator to relate power, voltage, and current. 

    I = \frac{P}{V} \\ P = \sqrt{3}\,V_{LL}\,I\,\mathrm{PF}
    • Where I is the current (amps)
    • P is the real power (watts)
    • V is the voltage (volts) for the basic (resistive/DC) calculation
    • VLL is the line-to-line voltage (volts) for a balanced three-phase system
    • PF is the power factor (dimensionless, typically from 0 to 1)

    For the basic (resistive/DC) tab, calculate current by dividing power by voltage: I = P / V.

    Definition

    What is an amperage drop?

    In most electrical contexts, “amp drop” is not a standard engineering term. In a simple series circuit, the current is (approximately) the same everywhere; what “drops” along a wire is voltage due to the wire’s resistance. People sometimes use “amp drop” informally to mean a reduction in current caused by lower available voltage at the load or increased resistance in the circuit. This calculator computes current, voltage, and power relationships (and includes a balanced three-phase option using power factor).

    Example Problem

    How to calculate current (amps)?

    The following example problem examines the steps and information required to calculate current using power and voltage (basic resistive/DC relationship).

    Assume the power is 20 watts and the voltage is 10 volts.

    Finally, calculate the current using the formula above:

    I = P / V

    I = 20 / 10

    I = 2 amps