Voltage drop calculator - Why you do not need this anymore

Just a few years ago all landscape lighting was halogen, before that, it was incandescent. The halogen bulbs ran hot and consumed a lot of wattage. Having transformers of 300watt, 600watt, and even 1200watts for large projects was not unusual. There were a lot of challenges, you needed very large and expensive feed wire to carry the current, and yes, there was voltage loss when you got to the end of the run. So your lights would be dimmer at the end, and burn out quicker near the transformer. For his reason, voltage loss charts and calculators were created plus all kinds of design time on large projects to make it all work correctly.

Then, LED landscape lighting came along and changed everything. For example, a 50watt halogen bulb has been replaced by a 7watt LED. So on a 300watt transformer, where in the past you could run 6 halogen fixtures you can now run 42 LED fixtures and get better light. In addition, LED lasts as much as 20 times longer than halogen and are available in “warm” color temperatures so they look great in your landscaping. See our videos for this.

So way back in the day, we made this video, "Outdoor LED Lighting, Transformer Load & Voltage drop explained" as we wanted to see the voltage loss (or lack of loss) on LED for ourselves. We think it will help explain voltage loss.

Now our engineer friends still say there is voltage loss but we rarely ever see someone trying to power 42 outdoor landscape lighting fixtures from one wire. It's just huge overkill but if they do they are most likely a pro and know what to do anyway.

Since the time of the video above, we have made over 100 new videos on landscape lighting, including topics on "how to install landscape lighting", "what landscape lighting looks like when it is done", "what low voltage outdoor landscape lighting looks like in the winter" as well as many troubleshooting video guides.

And if you still want to see the old voltage drop chart and calculator I have left it on this page below just for you.

If you plan to do landscape lighting we hope you do it with us. The results will be amazing and we are always looking for new great functional and affordable products to achieve success.

See our complete kits that make LED low voltage outdoor landscape lighting a simpler solution for your project!


This calculator is based on 120VAC in and 12VAC out for Halogen bulbs 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.