Inches Conversion

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" (a double prime)

(For example, six inches can be symbolised as either 6in or 6").

Unit of:


Wordwide use:

The inch is both an imperial unit and part of the US system of customary units and as such the inch has widely been used in the past. The inch is still a common unit in the US, and is popular in Canada and the UK. Japanese manufacturers such as Sony and T

There are still a few instances where inches are used internationally such as in the field of engineering and construction. Many countries, including the United States, still use inches for measuring dimensions and specifications in building plans, architectural drawings, and engineering designs. This is particularly true in industries that have strong ties to the United States, such as aerospace and automotive manufacturing. In these industries, inches are often used alongside metric measurements to ensure compatibility with American standards.

Another area where inches are still commonly used is in the production of consumer goods. Many products, especially those manufactured in the United States, are designed and produced using inches as the primary unit of measurement. This includes items such as screws, bolts, and other hardware, as well as tools and equipment. While metric measurements are becoming more prevalent in the global market, the use of inches in manufacturing remains significant, particularly in industries that have a long history of using imperial units.


Use of the inch can be traced back as far as the 7th century. The first explicit definition we could find of its length was after 1066 when it was defined as the length of three barleycorns. This was not a satisfactory reference as barleycorn lengths vary naturally. The British Standards Institute defined the inch as 25.4mm in 1930 in the document "Metric Units in Engineering: Going SI". In March 1932 the American Standards Association were asked to rule on whether to adopt the same value (at the time the American inch was 1/.03937 mm which approximated to 25.400051 mm). Because the values were so close, and because Britain has already settled on that value, the ASA adopted this value on March 13, 1933.

The inch is a unit of length commonly used in the United States and other countries that have not adopted the metric system. It is defined as 1/12th of a foot or 2.54 centimeters. The inch is further divided into smaller units, such as the half-inch, quarter-inch, and eighth-inch, which are commonly used in construction and woodworking.


The inch has been used as a unit of measurement in the United Kingdom since at least the seventh century, and in 1066 was defined as being equal to the length of three dried barleycorns placed end-to-end (a definition which survived for several centuries).

In the 12th Century the Scottish inch was defined as being equivalent to the width of an average man's thumb at the base of the nail. Similar units of measurement existed in many areas of what is now modern Europe, with the word for inch in Portuguese, French, Italian, Spanish and numerous other languages being the same or very similar to the word for thumb.

The English word inch derives from the Latin uncia, meaning one-twelfth part (an inch traditionally being 1/12 of a foot).

Even in the twentieth century various definitions of the inch were still applied around the world, although these differed by less than 0.001%. In 1930 the British Standards Institution adopted an inch of exactly 25.4mm, with the American Standards Association doing likewise in 1933, and the first country to legally adopt this definition was Canada in 1951.

In 1959 the United States and British Commonwealth countries signed a treaty agreeing to the standardised 25.4mm definition.

The English word inch is derived from the Latin word uncia, which means “one twelfth” – Because an inch was defined as being one twelfth of a foot. The word inch in other languages is often similar to the word ‘thumb’, as thumb width was a measure used to define an inch – for instance King David 1 of Scotland defined the inch as being “the breadth of the thumb of a middle sized man, measured at the root of the nail’ . In England we can find the definition of an inch as the length of 3 barleycorns in a statue of Edward 2nd in 1324.

Common references:

A United States quarter (25 cent) coin is just under one inch in diameter.

A fully-grown human eyeball is roughly one inch in diameter.

1 foot, 12 inches

1 metre, 39.37008 inches

45 RPM vinyl singles – the popular way to buy music from the 1960s to 1990s – Normally had a diameter of 7 inches. Long players (LPs) normally had a diameter of 12 inches

Rulers normally come marked for 30cm and 12 inches, since 12 inches = 30.048 cm

A can of Coke is 4.83 inches high

Usage context:

The inch is both an imperial unit and part of the US system of customary units and as such the inch has widely been used in the past. The inch is still a common unit in the US, and is popular in Canada and the UK. Japanese manufacturers such as Sony and T