Despite the fact that the whole world is striving for unification and standardization, individual countries continue to use their usual units of measurement. The metric system unites the peoples of the entire planet, but the UK and many English-speaking countries stubbornly hold on to their inches, yards and miles.
Sometimes the "fashion" for inches reaches us - for example, for some reason it is customary to measure the size of a television screen in inches. Therefore, in order to find out what an inch is and what it equals, you have to make some intellectual efforts.
What does the word "inch" mean?
Literally translated from English inch, or "thumb", means "thumb" . Inches came to our language, most likely, from German, in which "Daumen" also means thumb.
However, the Germans today use the metric system familiar to us, and the inch as the official unit of length remained in the UK. Obviously, it is based on the width of the male thumb.
Where and when did the inch appear?
The subjects of the British Queen have their own version of the origin of the inch as a measure of length. They believe that this unit is derived from the yard, which was equal to the distance between the thumb and the tip of the nose of the English king Henry I. However, according to another version of the legend, the length of one yard comes from the length of the sword of the aforementioned ruler. Well, an inch, in turn, is equal to one thirty-sixth of a yard.
If you examine the British codes and regulations, you will find another definition of an inch. In the Act of King Edward I, it is stated that it is equal to the length of three barley grains, laid close to the ends to each other. Moreover, the grains must be extracted from the middle part of the ear, and not from its tip or bottom. Until now, the English, when they talk about a length equal to a third of an inch, use the expression "barleycorn". Lengths expressed in inches are never written as decimals in England, and are expressed only as fractions with a denominator that is a multiple of 2. 
In Russia, there was also a measure of length based on the width of the thumb of the male hand. It was called the big line and consisted of ten ordinary lines (remember a three-line rifle: three lines are the caliber of a gun). They began to call the big line an inch after the reforms of Peter I, who, as you know, wanted to remake the whole country as soon as possible in a European way and did not know any measure in this. After the transition of the USSR to a much more convenient metric system, inches remained in the measurements of the diameters of water pipes and some artillery calibers inherited from the past.
What is 1 inch in centimeters?
In different years, the conversion of an inch to the metric system gave different values:
- in 1819 it was approximately 2.5400438 cm;
- in 1922 an inch was equal to 2.5399956 cm;
- In 1947, there were 2.5399931 cm in one inch.
But in 1958, for the convenience of calculations, it was established that one inch is equal to 2.54 cm, and since then only this number has been used to convert inches to centimeters.
What is an inch on a TV screen?
In Soviet times, television screens were measured in centimeters, since kinescopes for televisions were produced in our country. After its collapse, production was strangled by a flood of imports pouring in from abroad, mainly from the countries of Southeast Asia.
Since these countries have long been, and many are still under the influence of Britain and the United States, they use the British system of measures, and the screen size is measured in inches. Gradually, inches came into use with us when it comes to the diagonal of the television screen.
What is an inch in a phone?
Since mobile phones also have screens that are produced mainly in Southeast Asian countries, their dimensions are inevitably expressed in inches, and not in centimeters, which are familiar to us. Modern phones have screen sizes ranging from 3 to 7 inches. 
However, when choosing a phone, the screen size in inches is not the most important indicator, since it should be balanced with the density of the image in pixels. The higher this indicator, the better the quality of the picture you see on the screen.
