The fact that the U.S. has not adopted a metric system for quantities has two far-reaching consequences that impede learning basic math.
First is the very large number of different units that are in use and that require conversions. Length, for example, is measured in units of inches, feet, yards, miles, nautical miles and angstroms, and the conversions must be memorized to make sense of road signs, architectural drawings, etc. On the other hand, in the metric system only one fundamental unit is used for each quantity, and conversions are simple multiples of 10. We use the decimal system for money, although this was a significant departure from the British system, which had odd conversions between pounds, shillings, crowns, and pence until the 1970s. However, we have stuck with the Imperial system of units, even through a concerted push for metrication in the 1970s. Arguments used then that essentially killed the metrication effort are mostly irrelevant now, but the Imperial system remains.
The second consequence in remaining with the Imperial system is that length measurements are made in fractions of an inch. This results in the completely unnecessary need to manipulate fractions. Although most find it relatively easy to subtract a quarter from a half dollar, construction measurements, which typically use 1/16″ precision, are far more difficult. For example, try to solve the following problem in your head before working it out on paper.
11-5/16″ – 1-3/8″ = ?
This is the same as the following:
11.3125 – 1.3750 = ?
Except that tape measures that use decimals instead of fractions are rare, so the answer would need to be converted back to fractions in construction. However, it is likely that a construction problem using Archetecural Architectural Units will also include feet, resulting in a problem like:
3′ 1-5/16″ – 1′ 11-3/8″ = ?
This is solved by converting everything to one unit or by converting only as needed:
By fractions: 2′ 12-21/16″ – 1′ 11-6/16″ = 1′ 1-15/16″
By decimals: = 37.3125″ – 23.375″ = 13.9375″
So multiple conversions are needed. The same problem can be done much more easily using a metric tape measure:
947.74 mm – 593.73 mm = 354.01 mm
These types of calculations are for construction workers, who are paid to make them. But how about every day life in the kitchen? Converting a recipe for 4 to feed 7 can also involve significant math skills just on converting the various units of measure. Anyone living in any other country would be baffled by why we put up with such unnecessary complexity.
The most important consideration in why the adoption of the SI metric system is so critically important is that the Imperial system of units used in the U.S. is an enormous and unnecessary obstacle in everyone’s education. Of course our use of Imperial sizes in manufactured goods means that we cannot export these items because no other country in the world will take them, so switching to the SI metric system would be advantageous in terms of trade. There once was an argument that keeping Imperial sized products would keep manufacturing in the U.S., but most of it is already gone because other countries are happy to export to our market. Thus, there are significant economic benefits to switching to the SI metric system, but the most persuasive remains education.