Will be running power out of house 320 amp.double lug meter socket to garage 200 amp. Load center distance 180 ft. Question do I need a 200 amp. Disconnect box beside my meter socket to go undergroud to the garage? And what size cable is recommended for the 180 ft. distance?This will be underground.

You cannot come right out of the meter pan unless it is designed for it.
What panels do you have in the house? Do you really need 200A at the garage?

You cannot come right out of the meter pan unless it is designed for it.
What panels do you have in the house? Do you really need 200A at the garage?

It is a milbank 320 amp double load lugs designed for two load feeds.Could probably get by with 100 amp at garage.

So was it planned for one 200A panel in the house and one in the garage?
Or do you already have two 200's in the house?

The house is one 200 amp load center.

Then your feed to the garage is just like the one going to the house.

4/0AL or 2/0CU service conductors, and yes, you do need a disconnect at the house where the existing one is, and then another at the detached structure.

If you have a duoble lug meter pan, please do yourself a favor when you are going to hook the service panel in the garage up to it----Call the electric co to come and PULL the meter when you are going to connect it. If you are only using a 100 amp service panel in the garage, you can use 2/0 Al from the meter to the service pan. Use 2" Schedule 80 PVC conduit and follow all specs to bury it... your power co can give you the specs. You will also need another ground rod at the garage.
SAFETY!! Safety!! Safety!!