Just a simple calculation: the living space an elephant has in a zoo is about 500m2.

calculation 是名词，来自动词 calculate（计算）。calculate 由词根 calcul-（来自拉丁语 calculus，意为"小石子"，古代用小石子计数）和后缀 -ate（表示动作）组成。calculation 指"计算的过程或结果"。