Metric System Part of the Language
Go to just about anywhere that Spanish is spoken, and if you start talking using measurements such as pulgadas (inches) and pies (feet), you very likely won't be understood. Before you head out of the United States, take some time to learn the metric system. Not only is it easy to learn, but it also is understood in nearly every country in the world.

Comments
Well, you WILL be understood in Puerto Rico if you use pulgadas y pies.
In fact, if you go with metric, you very likely won’t be understood. Even if the highway distances are measured in kilometers (despite the fact that the speed limits are in mph!)
Thanks for pointing that out. There are exceptions to everything, aren’t there? And Puerto Rico is a special case.