Need 50amp at the Ranch, which romex ???

10/3 with ground. If running in conduit just run 4 10 guage wires THHN 1 each black, red, white, and green. Black and red are hot, white neutral, green ground.

Thanks for the fast responses, yes, we are adding 2 50 amp RV connections at this location, There are two poles and 2 panels to drop from, one on each corner of barn. Lucky for us.

We will be using conduit and running about less than 15 ft from each panel.

Since my son is a journeyman electrician, and I have learned a lot from him, you also need to consider how and where you are running the line. Will it be indoors or outdoors? Different romex types are called for depending on how that is answered. Can you run it in conduit? If, yes, then make sure the conduit it properly sized for the wire. Too small = heat build up = BAD. Also, do you need the full 50A? I would say yes if you are running 2 a/c's. If you are not, then maybe 30A would suffice and cut the cost on the wiring. Copper wiring has gotten pretty expensive, especially when you get to the larger sizes.

No 10/2 is 30 amp. You need 6/3 unless the run is very long.
Above link explains it all.

That is a two pole 240v breaker right?

Here is the info you need.
from myrv.us/electric