When used as a measuring unit (e.g. for temperature), the word always has the unchanged plural Grad: zwei Grad wärmer – "two degrees warmer"; einige Grad kühler – "some degrees cooler".
When not used as a measuring unit, the plural form is Grade: Die soziale Ungleichheit hat bisher ungekannte Grade erreicht. – "Social inequality has reached degrees so far unknown." This usage is less common than in English.