In addition to the metric system, there are other units of length that are still used in certain countries and contexts. The most well-known are the British and American units such as inch, foot, yard, and mile. These units were used long before the metric system was introduced and are still used today in the United States, the United Kingdom, and parts of aviation and maritime navigation.

 

 

British units of length

In the English system of length, inch, foot, and yard are closely related. One foot consists of 12 inches, and one yard consists of 3 feet.

 

Unit	Symbol	Relation	Equivalent in metres
inch	in	\( \large 1\ \text{in} = \frac{1}{12}\ \text{ft} \)	\( \large 1\ \text{in} = 0.0254\ \text{m} \)
foot	ft	\( \large 1\ \text{ft} = 12\ \text{in} \)	\( \large 1\ \text{ft} = 0.3048\ \text{m} \)
yard	yd	\( \large 1\ \text{yd} = 3\ \text{ft} \)	\( \large 1\ \text{yd} = 0.9144\ \text{m} \)

 

 

These units are still used in many practical situations, such as measuring human height in feet and inches, the length of golf courses in yards, and the size of television screens in inches.

 

 

Mile and nautical mile

The larger units of length, mile and nautical mile, are mainly used in transportation and navigation. A mile is used on land, while a nautical mile is used to measure distances at sea and in aviation.

 

Unit	Symbol	Relation	Equivalent in metres
mile	mi	\( \large 1\ \text{mi} = 1760\ \text{yd} \)	\( \large 1\ \text{mi} = 1609.344\ \text{m} \)
nautical mile	nmi	\( \large 1\ \text{nmi} = 1.852\ \text{km} \)	\( \large 1\ \text{nmi} = 1852\ \text{m} \)

 

 

Examples

 

• A person who is 6 feet tall is approximately \( \large 1.83\ \text{m} \).
• A football field in the United Kingdom is about \( \large 100\ \text{yd} \) long.
• A car travelling at \( \large 60\ \text{mph} \) moves at approximately \( \large 97\ \text{km/h} \).
• An aircraft measures its altitude in feet, for example \( \large 35\,000\ \text{ft} \approx 10.7\ \text{km} \).

 

 

Summary

 

• Inch, foot, yard, and mile are part of the British and American systems of length.
• These units are still used in countries that have not fully adopted the metric system.
• The nautical mile is used worldwide in navigation and is precisely defined as 1852 metres.

 

 

The alternative units of length show how different cultures have developed their own measurement systems. Today, the SI system is the common standard, but understanding these units remains important, especially in international contexts.