What is the amp rating for a 130 foot run of 8-4 romex?

Amp rating doesn't change regardless of length. Voltage drop is the issue and it affects motors, compressors etc. What are you planning on this circuit?

Installing a 7 ft. square spa with 220v motor and heater. Label on spa connecting box is stating 50A service.

Romex? Code for wiring pools and spas requires that the supply circuit includes a ground wire that's insulated and of equal size to the other wires. Romex does not meet this requirement.

Wow, OK, thanks. I'll check codes and a local supply house for what's needed. Thanks again.