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Why Didn’t the U.S. Adopt the Metric System? – Part 3 of a 3 Part Series

In Part 1 of this series, I explained how I became curious about the planned conversions from the Imperial to the Metric systems of measurement in Canada and the United States. In Part II, I provided a history of Canada’s laws that enforced the conversion and where the country stands now in utilizing the Imperial versus Metric measuring systems. Now, let’s examine the United States’ history regarding the metric system, followed by my opinion on why it failed to implement the planned conversion.

The United States is a muddled mess when it comes to its measuring system. This inconsistency and lack of follow-through dates back to our founding fathers and continues through our failure to complete the transition to the metric system in the 1970s.

History:

 When the American Colonies were being formed, the Founding Fathers decided to use an antiquated measurement system they inherited from the British Empire. Article 1, Section 8, of the Constitution of the United States provided that Congress should have the power “to coin Money… and fix the Standard of Weights and Measures.” Thomas Jefferson, Secretary of State in 1790, endorsed the use of a decimal system of measurement. The only fear was that the United States would be unable to verify the metric units without sending a delegation to France, which would be costly.

The metric system originated in France. The goal was to establish a uniform standard for all measurements and weights. The unit of length was a portion of the Earth’s circumference, and volume and mass were derived from the length unit. This was achieved by multiplying or dividing by 10 and its powers. Ten is much easier to work with than dividing by 16 (to convert ounces to pounds) or 12 (to convert inches to feet). The metric system is a decimal system with a base of 10, allowing for calculations by shifting the decimal point.

The French government officially adopted the metric system on April 7, 1795. A scientific conference was held from 1798 to 1799 to validate the system and design prototype standards, with representatives from Denmark, Italy, the Netherlands, Spain, and Switzerland in attendance. The adopted standards became official in France on December 10, 1799.

The United States was snubbed by France when it invited the other dignitaries to travel to Paris to learn the metric system in 1978. This snubbing was due to the U.S. entering into the Jay Treaty of 1796 with Great Britain, a French rival. France viewed this as a violation of its own treaty with the United States. It retaliated by seizing American merchant ships and refusing to invite them to the conference on the metric system.

The United States, having not taken part in this gathering, adopted the U.S. Customary System as our official form of measurement under Secretary of State John Quincy Adams in 1821. Part of the reason for this decision was fear that the metric system might fail following Napoleon Bonaparte’s reign during the early 19th century. Napoleon imposed the metric system on the countries he conquered, making it a symbol of French control. When European countries revolted against French control, they returned to their original means of measurement. Even with this revolt against France, the metric system continued to grow in popularity. By the end of the American Civil War in 1865, most of Europe had adopted the decimal-based measuring system.

The metric system was gaining popularity worldwide, and although we had not been invited to the 1798 gathering in France to learn about the system, President Andrew Johnson recognized its importance. In 1866, President Johnson signed the  Kasson Act, making it “lawful throughout the United States of America to employ the weights and measures of the metric system in all contracts, dealings, or court proceedings.”

France held another meeting of the world’s leading nations to discuss a new international version of the metric system, and the United States received an invitation and sent delegates. During the 1875 meeting, the United States and 16 other countries signed the Treaty of Metre, establishing the International Bureau of Weights and Measures. The treaty also created the International Committee for Weights and Measures to oversee the Bureau and the General Conference on Weights and Measures to consider and adopt changes. A lab in Sevres, near Paris, was selected to house the international metric standards. The U.S. received its copies of these documents in 1890.

The Mendenhall Order of 1893 stipulated that the fundamental standards for length and mass in the U.S. would be based on metric units. This means the U.S. officially and legally recognized the metric system 159 years ago when Tomas Jefferson, in 1790, endorsed the decimal system of measurement. That standard was confirmed 132 years ago with the signing of the Mendenhall Order.

Current U.S. Standards

If you are like me, you probably read those last two dates and went “what!!!” If this has been our standard for over 132-159 years, why are we still not using the metric system? In my opinion, it is a combination of laziness, unwillingness to invest financially in the change, and, most importantly, lawmakers who were weak in committing to the change and developing a law that would mandate the conversion. Here is what happened that led me to that thought process:

Fast forward 78 years from the entry of the Mendenhall Order to 1971. The United States is still operating under the Customary Imperial system. The U.S. National Bureau of Standards recommended in 1971 that the U.S. transition to the metric system over the course of 10 years. This would mean that by 1981, the country would be fully converted to the metric system. The first problem was the weak law that enacted this process.

The Metric Conversion Act was signed into law by President Gerald Ford on December 23, 1975. It states that the metric system is “the preferred system of weights and measures for United States trade and commerce.” Still, it permits the U.S. customary units in all activities. It states that all conversions to metric are “completely voluntary” rather than establishing the 10-year deadline recommended by the U.S. National Bureau of Standards. Schools began teaching children the metric system, and some businesses made the change; however, the majority of conversions never took place.

Due to the U.S. failing to complete the conversion to the metric system, conducting business with foreign countries became more difficult. In 1988, the Omnibus Trade and Competitiveness Act amended the 1975 Metric Conversion Act. Federal agencies were now required to use the metric system in business activities, including procurement grants, by the end of the 1992 fiscal year. It designated the metric system as the preferred standard for trade and commerce and assigned the Federal Government the task of helping industry make a voluntary conversion to the metric system. The problem is that the conversion remains voluntary, and the private sector has no obligation to implement the change.

The result of these non-mandatory laws is that they left the United States out of sync with the rest of the world. It also means that some industries made partial or complete changes, while made no change at all. The United States is a hub of various measuring standards that are not mutually compatible.

Today, the U.S. uses the SI (International System of Units) on a daily basis. About 30% of products manufactured in the U.S. use metric units. Pharmaceuticals are all metric, and beverages show both U.S. customary and metric units. Film, tools, and bicycles are metric. U.S. coins & currency are produced using metric specifications. Wine and distilled spirits have been using only metric measurements since the early 1980s. Packaging uses metric units to provide net quantity, nutrition, and health-related information for prescription drugs, over-the-counter medications, vitamin supplements, and other products. The U.S. lighting sector uses metrics for light output (lumens), peak beam intensity (candela), beam distance (in meters), and impact resistance (in meters).

Understanding Imperial Standards

This article begins with Part 1, which explains my curiosity about how our current measures were established. I’ve taken a wide-ranging approach to the subject, due in part to my curiosity and love of history, and partly because I believe that to understand where we are, we must know where we came from.

While all this history is fascinating, it still didn’t answer my question of how the Imperial System of measurements was established. These measurements appear to date back to around 450 CE (Common Era; a secular version of AD). It was then that the Germanic tribes invaded England and established a system of measurement that remains in use today:

  • An inch (ynce) was the length of three (3) barleycorns.
  • A foot was initially based on the length of a human foot. This led to inconsistencies in measurement, so the 12-inch foot was officially codified by King Edward II, likely because 12 has more factors, making it easier to subdivide for carpentry and construction.
  • A yard was established as a 3-foot construction standard.
  • An acre means a field and was considered the size of a field that a farmer could plow in one day.
  • A gallon represents the volume equivalent to eight pounds of wheat.
  • A mile was established by the British Parliament as eight (8) furlongs, or 5,280 feet. A furlong was a length based on a single furrow in a plowed field and was standardized by England’s government around 1300.

The United States is the only industrialized nation that hasn’t made the metric system compulsory. While cost is one factor, the main reason is the failure of Congress to make the metric system mandatory in all 50 states, the District of Columbia, and all U.S. territories. The U.S. made the conversion voluntary in laws enacted in both 1866 and 1975. The country has failed to adopt a unified system of metric measurement for transactions that affect the lives of ordinary citizens.

This has led to a hubbub of mixed measuring standards:

  • A football field is measured in yards, but footraces are measured using meters.
  • Mechanics use horsepower to measure an automobile engine’s power, but the same engine’s displacement is in liters.
  • Air pressure is expressed in pounds per square inch, which is equivalent to millibars for air pressure aloft, and inches of mercury for surface atmospheric pressure.

In the U.S. Customary System, there are over 300 different units used to measure various physical quantities. The failure of Congress to make conversion to the metric system mandatory has resulted in the U.S. being a hodgepodge of imperial and metric systems.

Basic Measurement Conversions:

1 mile = 1.6 kilometers.
1 foot (12 inches) = 30 centimeters
1 inch is about 25 millimeters or 2.54 centimeters
1 yard (3 feet) is almost 1 meter
1 kilogram is just over 2 pounds
1 pound is about 454 grams
In the U.K., 14 pounds = 1 stone

Converting Fahrenheit to Celsius is easy:
0 degrees Celsius (°C) is equal to 32 degrees Fahrenheit (°F)
24 degrees Celsius is equal to 75 degrees Fahrenheit
To convert Celsius to Fahrenheit, use the formula of (c x 1.8) + 32

If you want to know more, you can use the World Wide Metric Conversion Calculator for converting pressure, temperature, length, weight, and volume. Just enter the measurement you have, and it will fill in all other boxes within that area.

In closing, should the United States have enacted firmer laws mandating the change to metric? Do you think it would be better if we were on the same measuring system as the rest of the world, or do you like being a stand-alone country using the U.S. Customary System adaptation of the British Imperial System? Share your thoughts in the comments below.

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Why Didn’t the U.S. Adopt the Metric System? – Part 2 of a 3 Part Series

In Part 1, I explained how I became curious about the reasons the U.S. did not convert to the metric system at the same time Canada was making the change, leaving us as one of only three countries in the world that do not use the metric system of measurement. This section explains what Canada did to ensure it completed its commitment to switching from the Imperial to the Metric system during the late 1970s and early 1980s.

In January 1970, the “White Paper on Metric Conversion in Canada” established the Canadian government’s policy regarding its conversion to the metric system. The document specified that Canada would utilize a single, coherent measurement system based on metric units for all purposes. They then developed the “Weights and Measures Act” in 1971 to recognize the International System of Units (SI) for use in Canada. The “Consumer Packaging and Labeling Act” in 1971 required the use of the metric system on most consumer packaging labels.

The change from Imperial to Metric took time in Canada and began in the mid-1970s. I was a high school student in the United States and didn’t concern myself with what was going on in Canada. I do remember them telling us that we needed to learn the metric system because the country was changing to that form of measurement. I also recall that there were many objections to making the switch. We did incorporate some changes rather quickly, the main one being the switch to one- and two-liter bottles of soda. I don’t remember many other changes being made.

A look at how Canadians Measure

In Canada, things were rolling along at a gradual but steady pace:

  • Temperatures in Celsius beginning April 1, 1975
  • Rain and snowfall in millimeters and centimeters starting September 1975
  • Road signs showing speed limits in kilometers in September 1977
  • Speedometers and odometers in cars are manufactured in metric units beginning January 1979
  • Gas stations were pricing and dispensing gasoline and fuel in liters in 1979
  • Fabrics and home furnishings were required to be advertised and sold in meters and centimeters beginning in December 1980
  • Conversion of food weight measurements for advertising and pricing in metric units, starting December 1983.

We tend to assume Canada is solely metric, rather than the melting pot of systems that actually exist there. Canadians still use imperial units rather than metric in some areas. In 1985, Canada exempted some small businesses from the requirement of metric sales. Other requirements were also revoked, including the use of metric alone for measuring gasoline, diesel fuel, and home furnishings.

Even given these leniencies to a complete change, if you travel to Canada, be prepared for your speed limits and mileage signs to your next stop to be in kilometers, gasoline is sold in liters, and if grocery shopping, have a calculator/cell phone handy to make conversions from metric sizing to imperial sizing. This information is especially helpful when determining the size of ingredients for a recipe.

Being a lifelong resident of the United States, I didn’t delve as deeply into Canada’s history of its measuring system conversion as I did into my own country’s. Watch for Part III, where I’ll give the United States’ history and why it failed to complete the conversion.

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Why Didn’t the U.S. Adopt the Metric System? – Part 1 of a 3 Part Series

Listening to a weather forecast on a Canadian TV station, the temperatures are given in Celsius. Paul, who grew up in Canada, makes the mental conversion easily. Paul grew up using the Imperial system of measurement, which is used in the United States. After he was an adult and had immigrated to the U.S., Canada converted to the metric system. Paul is an electrician, a profession that uses the metric system of measurement. That, combined with his frequent travel to Canada, means he is familiar with both systems and believes the metric is a more accurate means of measurement.

Paul frequently comments that the U.S. was supposed to make the conversion to the metric system when Canada did, but failed to fulfill their promise. I recall being in grade school when we were told that the United States would adopt the metric system. I wondered how valid Paul’s repeated comment was, so I delved into researching the topic.

 Canada was making the transition at the same time and completed their conversion between 1970 and 1985. The United States never finished the conversion, despite agreeing to do so, and continues to use the Imperial System today. That made me wonder, why did Canada succeed, and we didn’t?

In my opinion, the U.S. failed to complete the conversion due to a lack of effort and unwillingness to invest in implementing the change. Businesses opposed the cost of having to retool and adjust standardized measurement systems, including bolts, pipes, and nuts, to metric measurements. The Metric Conversion Act of 1975 [ https://usma.org/laws-and-bills/metric-conversion-act-of-1975 ] made the metric system preferred, but not mandatory. This, combined with public resistance and the government’s inability to enforce the change, led to the failure to implement the change.

As of today, the United States is only one of three countries (the United States, Liberia, and Myanmar (Burma)) worldwide using the Imperial measurement system. The Imperial system [ https://www.britannica.com/topic/Imperial-unit ] (also known as the British Imperial system) originated from the British Empire, which ruled many areas of the world between the 16th and 19th centuries. Although the U.S. Founding Fathers made numerous changes in governing style when obtaining independence from Britain, they decided to maintain the Imperial system of measurement, despite the metric system growing in popularity.

A chart showing the Imperial vs Metric measurement and weight differences.

Rather than adopting it in its original state, the United States devised its own version of the Imperial system, known as the U.S. Customary System. It uses measurements of feet, pounds, and miles, but differs slightly from the British Imperial system. The most substantial difference is in volume:

  • The U.S. Customary fluid ounce is 29.573 ml; the British Imperial fluid ounce is 28.413 milliliters.
  • The U.S. Customary pint is 473.176 ml (16 fl. oz); the British Imperial pint is 568.261 ml (20 fl. oz).
  • The U.S. Customary quart is 0.94 L (32 fl. oz); the British Imperial quart is 1.13 L (40 fl. oz).
  • The U.S. Customary gallon is 3.78 L (128 fl. oz); the British Imperial gallon is 4.54 L (160 fl. oz).

The reason for creating the Customary version of the Imperial system was that the metric system was not yet fully developed. The Founding Fathers had a desire to establish a unique national identity and infrastructure, and tweaking the system to make it unique to the U.S. was their way of achieving this goal.

Myanmar (Burma) and Liberia use the Imperial system but are transitioning to the metric system; neither has a predicted completion date. Once their conversions are final, the U.S. will be the sole user of the Imperial system. In 2021, the British government announced plans to return to the Imperial system during its exit from the European Union. The changeover began but was abandoned in 2024 after consulting with the public and discovering overwhelming support for using metric units. They do still use the imperial system for things such as beer sales, road speed, and distance signs, and body measurements.

Although I found the metric system difficult to learn as a child, our government failed its citizens by not enforcing a complete change in the 1970s. A full conversion would have served business owners better in international trade negotiations and put us on equal terms with all foreign lands in understanding measurements when traveling.  

All countries worldwide, including the U.S., Myanmar, and Liberia, have adopted or legally sanctioned the International System of Units (SI), the modern form of the metric system. Canada and the United States are both melting pots of the Imperial and Metric measurement styles.

Watch for Part II and Part III in upcoming blogs, which will deal with the law and the Canadian conversion, the laws and the United States conversion, and where the United States stands today.

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