For non-Americans, there are many difficult things to be adapted to their lives during staying in the USA. Besides the language barrier, one of the most difficult things could be the weights and measures. Most of the world uses the metric system which is the international standard units. However, the USA does not use metric system, so many foreigners need to calculate the US customary units to metric units for understanding. Also, for Americans, there are many problems caused by using different units, but it is not easy to adapt to the metric system.