Why does strain have no units?

It is a ratio of two lengths so the units cancel.

Hi Jena! The strain of a material is found by dividing how much a material has stretched over it's original length. For example, if a 2 meter wire is stretched by 0.05 m then the strain will be 0.05/2 = 0.025. Because both values have the same unit they cancel each other out when you divide them. This means that the strain value has no unit. Hope that helps.