Needless to say, a U.S. transition to the metric system has been a little slow.
We've made some headway. The scientific community generally recognizes that the metric system (or the International System of Units) is way more logical and intuitive, and more businesses are converting to metric all the time.
Yet many Americans are still very reluctant to use the system in their everyday lives. Could they have some good reasons?
Metric system is flawed
The meter was initially defined as one ten-millionth of the distance from the pole to the equator. Now length of a meter is tied to the speed of light in a vacuum, which is something that can always be found in nature and will never change.
Almost all of the metric system's units have now been linked to some sort of universal constant, except one--the kilogram. Originally, a kilogram was defined as the mass of a cubic decimeter of water. Later, the experts forged a cylinder of mostly platinum and declared it to be exactly one kilogram. This hunk of metal has been used to calibrate the world's scales ever since.
However, earlier this year, the International Committee on Weights and Measures finally met to discuss the kilogram and its lack of a constant. The committee recommended the use of Planck's constant, but the new standard has yet to be made official.
I should also point out that most of the imperial units are solely defined according to the metric system. Yes, an inch is literally 2.54 centimeters--no natural constants attached.
Metric system isn't practical
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.
There may be better options
Before we consider going to all the trouble of adopting a new measurement system, shouldn't we be sure that the metric system is the best option? One physicist, Johannes Koelman, has proposed another alternative to the imperial system that he has dubbed the "post-imperial" system.
The post-imperial system takes advantage of some coincidental properties of the pound and the inch. It uses these properties to fix a couple things that the metric system lacks. Both of these repairs involve time.
Unlike the metric system, Koelman's model measures time using the same units as distance. This feature relieves us from having to do calculations involving miles per hour or meters per second. It also incorporates the fact that time is simply a fourth dimension of our 3D world.
Even though Koelman's idea would be hard to implement, it has some very useful features and opens the door to other possible alternatives.
Imperial system is more quirky
As you may have noticed, the witches and wizards at Hogwarts don't use the metric system. Harry's wand, for instance, is described as eleven inches long (also niiiice and supple). This is not simply an adaptation for the U.S. edition. In fact, despite her editor's protests, J.K. Rowling insisted that even the British editions keep the imperial system.
After recalling the wizards' system of currency (29 knuts to a sickle, 17 sickles in a galleon), it's not difficult to understand Rowling's decision. She says that the imperial system is much more quirky and therefore is better suited to the wizarding world.
Rowling even accepted an invitation to become a member of the British Weights and Measures Association. She admits, however, that she accepted the invite as a joke, and that she really does prefer the metric system.*
Imperial system is traditional
I think the main reason why Americans are reluctant to make the metric plunge is simply because they are afraid to change their ways. Maybe it's a valid reason.
Mathematics professor at Chapel Hill, Russ Rowlett, says "In fact, the metric system has met popular opposition in every country at the time of its adoption. People don't want to change their customary units, which are part of how they see and control the world. It is naturally disturbing to do so."
*This information was written by J.K. Rowling and is summarized from the Pottermore beta site, Book 1, Chapter 1, "Measurements" 1 and 2.