It depends on the voltage of the circuit you're calculating the voltage drop for. 120V

You would enter 120V if you're calculating the voltage drop for a

120V circuit. This is typical for standard residential outlets, lighting, and small appliances. 240V

You would enter 240V if you're calculating the voltage drop for a

240V circuit. This is typically used for larger appliances like electric stoves, dryers, water heaters, and some air conditioners.

Why is it important to use the correct voltage?

Voltage drop is directly related to the current flowing through the wire and the wire's resistance. Because power (watts) is equal to voltage times current (P=VI), the current flowing through a 120V circuit delivering the same power will be higher than the current flowing through a 240V circuit. Higher current leads to greater voltage drop for the same wire gauge and length.The voltage you enter is critical because the calculator uses it to determine the current that will be flowing through the wire for a given load (amperage or wattage). If you use the wrong voltage, the calculated voltage drop will be incorrect, potentially leading you to undersize the wiring and create a fire hazard or cause equipment malfunction. Flag for review