Tim Radney enumerates the tiers available to us with Azure SQL Database:
When Azure SQL Database first launched, there was a single pricing option known as “DTUs” or Database Transaction Units. (Andy Mallon, @AMtwo, explains DTUs in “What the heck is a DTU?“) The DTU model provides three tiers of service, basic, standard, and premium. The basic tier provides up to 5 DTUs with standard storage. The standard tier supports from 10 up to 3000 DTUs with standard storage and the premium tier supports 125 up to 4000 DTUs with premium storage, which is orders of magnitude faster than standard storage.
But there have been several additions since then and Tim lays it out for us.