Which Imperial Units Are Still Legally Used Instead of Metric

It is a common misconception that all countries have completely transitioned to the metric system for all measurements. While the majority of nations have adopted the metric system, some still retain certain imperial units in specific contexts. This includes the United States and the United Kingdom, where certain imperial units are permitted by law for specific applications, despite a general shift towards the metric system.

United States

In the United States, the legal landscape surrounding units of measurement is unique. While the US Customary System coexists alongside the metric system for trade and legal purposes, there are specific instances where imperial units are still used.

Perhaps the most notable example is the imperial units of length, which are still in use for various applications. These include:

Miles: Primarily used for road distances. Feet and inches: Used for construction and other building-related activities. Yards: Common in sports and agriculture.

The US maintained these traditional units after gaining independence from Britain in 1776. The National Institute of Standards and Technology (NIST) provides detailed information on the legal status of these units, noting that while the metric system is preferred for many scientific and trade applications, the governmental and legal professions continue to use the US Customary System for official documents.

United Kingdom

In the United Kingdom, the shift towards the metric system has been more widespread, but there are still a few imperial units that are legally permitted for specific uses.

Miles: The UK retains miles for road distance signs, though this is primarily due to a decision made to align with the United States and other road distances that use miles. For example, danger speed limit signs often use miles to match US standards. Pints: Pints are still used in the UK for measuring liquids sold in pubs and supermarkets. This is a traditional measure that has been in use for centuries. Carats: Carats remain the standard unit of measurement for precious metals, particularly in the jewelry industry.

The UK officially transitioned to the metric system in 1824, following the British Weights and Measures Act. However, there have been specific exemptions and areas of resistance, particularly in fields where tradition and historical usage are deeply ingrained.

Imperial Threads and Hose Conversions

Besides units of length, the British Standard Pipe (BSP) thread is still in use for plumbing and other applications. This thread, which predates the adoption of the metric system, has been adapted into metric numbers but retains its original imperial measurements. This system is supported by industry and has been a part of the plumbing industry for over a century.

A great example of the resilience of imperial units is the garden hose. Despite the widespread adoption of the metric system, a garden hose can still be screwed onto a hose bib that was made 120 years ago. This is due to the use of the British Standard Pipe (BSP) thread, which is not a metric system but a renumbering of the original imperial thread.

The BSW (British Standard Whitworth) is another version of this thread, known to people who work on old British vehicles and machinery. The persistence of these traditional threads in modern applications highlights the longevity and practicality of these imperial units.

Conclusion

While the global trend towards the metric system is undeniable, certain imperial units in the United States and the United Kingdom continue to be legally utilized in specific contexts. These units, such as miles, pints, and carats, remain a part of the cultural and historical fabric of these countries. Understanding the legal and practical implications of these units can help businesses and individuals navigate the unique measurement landscape of the US and the UK.