Why the United States Doesn’t Use the Metric System

Wondering why the United States is one of three countries in the world that doesn't use the metric system? The answer will definitely surprise you.

Have you ever noticed that the standard system of measurement tends to change when you exit the United States? Clothing sizes are often measured in centimeters instead of inches, distance is measured in kilometers over miles, and volume is measured in liters rather than ounces. Although English is used in many countries across the globe, when it comes to measurement, it can often feel like there’s a language barrier between Americans and the rest of the world. You may think that this is an overstatement—there must be some other countries that don’t use the metric system, right? However, in reality, there are only three countries in the entire world that don’t use the metric system—and the U.S. is one of them!

Considering how often America interacts with other countries about crucial measurements, it may seem strange that they have not adopted the most ubiquitous system of measurement in the world. So, why doesn’t the U.S. use the metric system? And find out why it uses Fahrenheit instead of Celsius, too!

What is the metric system?

For most Americans, the metric system is one of 31 things you’ve probably never thought about. Before we can understand why the U.S. does not use the metric system, it’s important that we understand what the metric system is—and how it differs from the U.S. customary units. The metric system, also known as the International System of Units (SI), is a system of measurement that is built on three main units: meters, liters, and grams. Since the metric system is a base 10 system of measurement, each succeeding unit of length, mass, or volume is 10 times larger than the previous one. The names for these units are the combination of a prefix—which indicates the size of the unit—and a base—which tells you whether the unit is measuring length, mass, volume.

Still don’t get it? Let’s break it down. In the metric system, meters are the base unit for measuring length, which means that each preceding or succeeding unit will contain the base name, “meter” along with a prefix that communicates its size. For context, a meter is equivalent to three feet, three inches long. So, a decimeter is 10 times smaller than a meter, a centimeter is 100 times smaller than a meter, and a millimeter is 1,000 times smaller than a meter. Conversely, a dekameter is 10 times larger than a meter, a hectometer is 100 times larger than a meter, and a kilometer is 1,000 times larger than a meter. Although we could easily measure the length of a football field in meters, it would not make as much sense to measure the length of a computer in meters. Since a computer is less than one meter long, we would use a smaller metric unit, such as centimeters or millimeters to express its length. The same rules apply when measuring the mass and volume of matter, using grams or liters respectively. Get to the bottom of these science “facts” that are actually false.

What are the U.S. customary units?

Now that we’ve established how the metric system works, it’s important to understand the difference between the metric system and the U.S. customary units. While the U.S. system also measures length, mass, and volume, it uses an entirely different set of units than the metric system. Plus, unlike the metric system, U.S. customary units do not follow a “base” system of measurement. Instead, when measuring the volume of a liquid using U.S. customary units, we use fluid ounces, cups, pints, quarts, and gallons—with fluid ounces being the smallest unit of measuring volume and gallons being the largest unit of measuring volume, respectively. One gallon is equal to four quarts, which is equal to 8 pints, which is equal to 16 cups, which is equal to 128 fluid ounces. Simple, right?

Since there is no “base” rule for U.S. customary units, volume, mass, and distance are all measured differently under this system. The U.S. customary units for measuring the mass of an object are ounces, pounds, and tons. In this category of measurement, the smallest unit of mass is an ounce, the next smallest unit is a pound, and the largest unit of mass is a ton. Specifically, one pound is equal to 16 ounces, one ton is equal to 2,000 pounds, and one ton is also equal to 32,000 ounces.

The last type of measurement under the U.S. customary units is length, which is measured in inches, feet, yards, and miles. Under this system, the smallest unit of length is inches and the largest unit of length is miles, respectively. Since this is arguably the most commonly used measurement in everyday life, most U.S. residents know that there are 12 inches in one foot, three feet in one yard, and 1,760 yards in one mile. Bottom line? Despite the fact that both systems of measurement have the exact same purpose, U.S. customary units are entirely different from the metric system. Never learned this difference in school? You’ll be shocked by these 15 other fascinating facts about America you never learned.

Why doesn’t the U.S. use the metric system?

Scientific measuring cup or beakerPhil Lewis/shutterstockAs of today, the entire world has adopted the metric system, with the exception of the United States, Myanmar, and Liberia. Given the fact that it is time-consuming and tedious to translate between U.S. customary units and the metric system, having two competing systems is not ideal for global communication and cooperation. So, why doesn’t the U.S. use the metric system? Surprisingly, the answer actually dates back to the 1700s.

In 1790, France conceived the metric system as a means of streamlining commerce, reducing fraud, and clearing up the general confusion that permeated the country in the absence of a standard system of measurement. The first step in creating this system was setting a universal guide for measuring a meter. Since the French scientists wanted to be as precise as possible and enable others to emulate their process, they decided to derive the measurements from the earth’s circumference—a well-known dimension at the time. To do this, the scientists selected a longitudinal segment of the Earth that ran between the northern and southern parts of France, and carefully divided it to create the meter. The resulting measurement system, which is now known as the metric system, was extremely innovative and attractive to the international community. However, since the metric system was rooted in a portion of French land, the United States decided not to adopt this system.

In the 19th century, as the rest of the world began to accept the metric system, the U.S. Congress proposed that the country transition toward this international system as well. However, at this point in time, American industrialists had already stocked their factories with equipment that was based on the U.S. customary units. To prevent a costly overhaul of their equipment, these industrialists used their influence to stop Congress from adopting the metric system throughout the 19th and 20th centuries. Today, America still teaches U.S. customary units in its schools, although many scientists and organizations have submitted to the ease of the internationally used metric system. America’s dedication to the U.S. customary units is not the only convention that the country has held onto throughout the years. Next, find out why Americans and Brits drive on the opposite side of the road.


Carley Lerner
Carley Lerner is a freelance writer and former editorial intern for Reader's Digest. She is a member of the Class of 2021 at Duke University, where she writes for the school newspaper, The Chronicle.