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Voltage Drop Calculator

This calculator is based on 120VAC in and 12VAC out and is for use as a guide only to help you begin your lighting project. We strongly recommend checking the actual voltage at each fixture with a volt meter before burying and finalizing your project.

  • For best results layout out your wire run according to the design specifications.
  • Connect all the fixtures and take voltage readings at the fixtures to ensure proper voltage.
  • If readings are within proper voltage requirements for the fixture proceed on finalizing your project.

We accept no responsibility for the use of the information provided.

To use this calculator select the gauge of wire you will be using for the run, enter the total wattage on the run (simply add up all the light bulb wattage that will be on that run) and lastly enter the length of the run. Click calculate. Voltage drop is the amount of voltage lost due to resistance in the wire. Voltage is the remaining voltage after voltage dropis subtracted out. See below for acceptable voltages for LED and typical incandescent landscape lighting systems.

If the majority of your light fixtures are at the far end of the run, multiply the voltage drop by 1.5 (150%).

  • Gauge:
  • Wattage:
  • Length:
  • Voltage Drop: ???
    Voltage: ???

For LED lighting systems check the maximum and minimum voltage required to power the fixture. Typically anything higher than 8.5 volts is acceptable but should not exceed the fixtures maximum voltage requirements

For traditional incandescent lighting systems please refer to the chart below.

Voltage Rated Lamp Life Candlepower %
13.2 2/3 350
12.6 3/4 180
12 1 100
11.5 2 times 80
11 3 times 75
10.75 4 times 70
10.5 5 times 65
10 9 times 50

How to read this chart:
Example 1:

Lamp life is rated at 3,000 hours - Voltage is at 12.6 - Candlepower or light output will be 180%. At these specs the rated lamp life will drop to about 2,250 hours but be 80% brighter than what the lamp is rated.

Example 2:

Lamp life is rated at 3,000 hours - Voltage is at 10.75 - Candlepower will be 70%. At these specs the rated lamp life will increase 4 times

For the voltage drop chart click here.