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US Customary System

Written by the Fiveable Content Team • Last updated September 2025
Written by the Fiveable Content Team • Last updated September 2025

Definition

The US Customary System is a system of measurement units that is widely used in the United States. It is the primary system of measurement for everyday purposes, such as in the measurement of length, weight, volume, and temperature, and is the basis for many of the units commonly used in the country.

5 Must Know Facts For Your Next Test

  1. The US Customary System is based on the English Imperial System, which was used in the United States prior to the adoption of the metric system.
  2. The US Customary System is not the same as the International System of Units (SI), which is the modern metric system used in most countries around the world.
  3. The US Customary System is widely used in the United States for everyday measurements, but the metric system is used for some scientific and international applications.
  4. The US Customary System includes units such as inches, feet, yards, miles, ounces, pounds, cups, pints, quarts, and gallons.
  5. The US Customary System is often criticized for its complexity and lack of a consistent, decimal-based structure, unlike the metric system.

Review Questions

  • Explain the historical origins of the US Customary System and how it differs from the metric system.
    • The US Customary System is based on the English Imperial System, which was used in the United States prior to the adoption of the metric system. Unlike the metric system, which is a decimal-based system with consistent units, the US Customary System is more complex, with a variety of units that are not always related to each other in a consistent way. This can make it more challenging to convert between different units of measurement, which is one of the key criticisms of the US Customary System compared to the more straightforward and widely used metric system.
  • Describe the common units of measurement used in the US Customary System and how they are related to each other.
    • The US Customary System includes a variety of units for measuring length, weight, volume, and temperature. Some of the most common units include inches, feet, yards, and miles for length; ounces, pounds, and tons for weight; cups, pints, quarts, and gallons for volume; and Fahrenheit for temperature. While these units are widely used in the United States, they are not always related to each other in a consistent, decimal-based way, unlike the metric system. This can make it more challenging to convert between different units of measurement within the US Customary System.
  • Analyze the advantages and disadvantages of the US Customary System compared to the metric system, and explain why the US has maintained the use of the US Customary System despite the widespread adoption of the metric system in other countries.
    • The US Customary System has some advantages, such as being deeply ingrained in the culture and everyday life of the United States, and providing a familiar set of units for many Americans. However, it also has significant disadvantages, such as being more complex and less consistent than the decimal-based metric system, which can make it more challenging to perform calculations and conversions. Despite the widespread adoption of the metric system in most other countries, the US has maintained the use of the US Customary System, in part due to the significant cost and effort that would be required to transition the entire country to the metric system, as well as cultural inertia and resistance to change. Ultimately, the continued use of the US Customary System in the United States reflects a balance of practical considerations, cultural factors, and the challenges of implementing a large-scale change in the country's measurement system.