When running wire from electrical box to hot tub should I use conduit (outdoor) or is there under ground rated 240v wire. Also what is appropriate wire size?

TKRussell may be able to give you a part number for the 50amp GFI breaker made for spas. You must install this in your panel or a new sub panel. They are big. He recommends #6 wire and it does not have to be inside conduit but its not a bad idea. You can buy the appropriate #6 wires that is insulated and rated to be buried as is.

When running wire from electrical box to hot tub should i use conduit (outdoor) or is there under ground rated 240v wire. Also what is appropriate wire size?
Yes you could us pvc under ground pipe but there also is cable you can get. Go to the hard ware store and ask for mineral insulated cable rated for 240v and they should have some. The wire size will vary from probably # 8-#4 . I matters if you use aluminum or copper wire.

It depends on your hot tub ampacity requirements? Note: Never run wire for a hot tub unless you know this information.

Is your hot tub indoors or outdoors?

Need more information

I guess when you say "Hot Tub", I'm thinking Heater.
I would Run 3/4" PVC, 2-#6's for hots, 1 #8 for Neutral, #10 for ground, this will be coming from GFI, no closer than 5' and in sight. I would verify any local codes,
On maximum and in sight, I have heard different for different areas. We can't bury cable,
Or use Aluminum.

Yep, 95% of them are 220 due to the heater. I have seen a few personal hot tubs that are 110 but so rare and tiny I tend to not think of them.

I agree with Washington, we need more detail before offering any advice concerning wire sizes, amperages, etc. While we are all eager to help, the person asking the question has the responsibility of providing accurate information to receive an accurate answer.

I forgot to mention, size breaker accordingly, and like above, without more info, maybe gas heater?
That is how I would wire mine, Even if it was 120, the #6's should hanlde the load.
I am getting older and don't like to redo something twice.
Do it one time right, and forget about it.