SQL - how to count unique combination of columns

I'm not sure if this is possible but I want to count the number of unique value in a table. I know to count the number of unique folderIDs I do:

select count(folderid) from folder

but I want the count of the number of unique combination of folderid and userid in the folder table. Is there a way to do this?

select count(*) from (
  select distinct folderid, userid from folder
)