Cable size for 240 volt/50 amp hot tub

For installations that need to conform to the National Electrical Code, you must use their guidelines. Contact your local electrician to find out what is legal.

You need to get the grounding right too. Water + electricity=danger. You may invalidate your insurance and/or kill someone if you don't know what you are doing. Get an electrician. If I was thinking of buying a house with a hot tub, I'd demand to see an electrician's certificate.