Before looking into why Americans can't adapt themselves to the metric system, let us take a glimpse on how they get into imperial system of measurement.
In the year 1790, the United States entered into its first phase of industrial development. When they were in need of a metric system for all their factory needs, the newly developed French metric system (the one commonly used around the world) made its way to the US attention.
Academic Joseph Dombey set sail from from Paris with the new metric system in hand, a rod measuring exactly a meter and a copper cylinder weighing one kilogram. He was journeying all the way across the Atlantic to meet the US Secretary of State Thomas Jefferson.
A storm rolled in knocking Dombey's ship off course. The poor scholar was washed away in the Caribbean and attacked by the British pirates. His belongings were seized and auctioned. By this time US started to adopt the British Imperial system of measurement.
France sent a second representative to promote their metric system. But by the time, Jefferson was not there. The new Secretary of the State Edmund Randolph did not care much for measurement.
Since then, the US has had many opportunities to change to the metric system which is praised as more logical and simple.
So, Why Americans has not changed it?
The biggest reason is changing everything to the metric system costs more time and money. For example, NASA engineers recently reported that converting the space shuttle's relevant drawings, software and documentation to metrics would require $370 million - about half the cost of a typical space shuttle launch.
Whenever the discussion of switching unit systems arose in Congress, the passage of a bill favoring the metric system was opposed by big businesses and American citizens who didn’t want to go through the expensive and time-consuming process.
It is also believed as an American stubborn attitude. They treated themselves to be unique. Even though it is tough, they wanted to set a system different from other countries, symbolizing its status as a leader rather than a follower.
However, the most logical explanation is just the failure of Congress to make the metric system mandatory in all the 50 states.
Imperial system vs Metric system
1 mile = 1.6 Kilometers.
1 foot (12 inches) = 30 centimeters.
1 inch = 25 millimeters or 2.54 centimeters.
3-foot = 1 meter(almost).
1 pound = 0.454 kg.
0 degrees Celsius = 32 degrees Fahrenheit.
24 degrees Celsius = 75 degrees Fahrenheit.