What is voltage drop?
Voltage drop is the decrease in electrical potential across a component — such as a resistor, a length of wire, or a connector — as current flows through it. Understanding voltage drop is essential for designing circuits and sizing wiring so that devices downstream receive enough voltage to work correctly.
The formula
Voltage drop follows Ohm’s Law directly: V = I × R, where I is the current in amps and R is the resistance in ohms. The power dissipated as heat in that resistance is P = I² × R.
Enter the current and resistance to get the voltage drop and power dissipated. If you also enter a supply voltage, the calculator shows how much voltage remains after the drop and what percentage of the supply is lost across this resistance. This tool is for general electrical planning and education, not a substitute for a qualified electrician on real installations.