Need help deciding if this can be done - length of wire run

[Ghostrider]

This will be a DIY project if I can figure out whether it can be done or not. I
have searched a lot of websites and am not a good way to determine this. I am planning on adding low voltage lights to the back, side and front of my house, Because the only plug is in the back I need to run about 175 feet after the transformer. I plan on having about 20 lights of around 7 watts. I cannot find a good way to determine if a 300 watt transformer will run this. I roughly calculated a voltage drop of around 2 volts depending on guage. The problem is a lot of website say that 12 guage will go 200 feet. None of them say whether a 12 volt light will work at the end. Is this doable with 12 guage or 10 guage or am I wasting my time and need to run an underground 120 volt line to reduce the distance?

[sitelights]

There are many posts that address the topic of your inquiry. The site search engine will lead you to posts covering voltage drop, wire length and size as well as properly sizing transformers, and so on using the appropriate keyword. To start you may want to look at "transformer options" in the Transformer Forum.

[LowVoltPro]

175ft at 140 watts would require a 19volt tap on 12/2 cable , a 17v tap on 10/2 cable and a 15v tap on 8/2 cable.