While the metric units’ association with physical constants makes them accurate, it makes them less practical for common use. The units of cups and tablespoons developed naturally because these objects were right there in the kitchen. The gram, on the other hand, was not developed with cooking and baking in mind, so it is much smaller than it needs to be. For the same reason, the foot and the ounce are also much more user-friendly than their metric counterparts. Also, because they have a base of ten, metric units cannot be divided into as many even fractions as imperial units. A meter can only be evenly divided into 2 or 5, while a foot can be divided into 2, 3, 4, or 6.

So if you ever have to measure a third of a meter, good luck.