Voltage Drop Calculator

Low Voltage Lighting Volt Drop Calculator - Use this calculator to estimate voltage drop in low-voltage lighting circuits. There are 7 inputs: 1. Rated load voltage ... this value will almost always be 12v. 2. Number of fixtures. Enter the number of fixtures on the run. 3. Watts per fixture. Enter the watts per fixture. If the fixtures have different wattage rating, use the average. 4. Circuit length to the first fixture. 5. Circuit length to the last fixture. 6. Supply voltage ... select the voltage of the tap. 7. Wire size (AWG). Real world tests show these values to have an accuracy between 94% and 97%.

Load Rated Voltage Volts Number of Fixtures Watts per Fixture (at Rated Voltage) Watts Amps Total Watts & Amps (at Rated Voltage) Watts Amps Circuit Length to First Fixture Feet Circuit Length to Last Fixture Feet Supply Voltage Volts Wire Size AWG Load Center Feet Average Fixture Spacing Feet Circuit Length Occupied by Fixtures Feet % % of Concentrated Load Volt Drop % First Fixture Last Fixture Wire Loop Resistance Ohms Ohms Volt Drop (Loop) Volts Volts Voltage at Fixture Volts Volts

Special Thanks This calculator is based on the original Low Voltage Lighting Volt Drop Calculator v2.4 created by Ed Lethert of Ed Lethert Associates, Inc from 11/29/2006. His clear engineering approach and practical calculations have helped designers, installers, and engineers understand and manage voltage drop in real-world low-voltage lighting systems for many years. This updated version preserves the original intent and math while adapting it for modern web use. Many thanks to Ed for making this work available, the lasting value it continues to provide and his permission to republish.