Convert millimeter to inches

Symbol

The millimeter is represented by the symbol "mm." 

Description

Millimeter is an SI (International System of Units) unit of length. It is usually the smallest measure in rulers of the metric system.The word "milli" is derived from the Latin word mille, which means one thousandth. Therefore, a meter is equivalent to a thousand times a millimeter.

The international definition of meter which is the SI base unit of length, is the length of path that light takes in the vacuum over a period of 1/299 792 458 of a second. Thus, 1 millimeter is equivalent to 1/1000 meter. That implies that a millimeter is the distance that light travels in the vacuum in 1/299792458000 seconds.

Following that, there are 10 millimeters in a centimeter and 100 millimeters in a decimeter. In the other direction, a millimeter is equivalent to 1/10 centimeters. A millimeter is also equivalent to 1000 micrometers.

Interestingly the smallest dimension human eyes can detect is about 0.02 to 0.04 mm. This is about the thickness of human hair!

History

The term millimeter was first used in the late 1700s. It was introduced during the development and adoption of the metric system of weights and measures in France in 1795.

The first recorded use of the millimeter was in the Journal of Natural Philosophy in 1797, according to OED (Oxford English Dictionary).

Use

Millimeter is a very small unit of measure. Therefore it is usually used for measuring minute dimensions. 

Symbol

The inch is represented by the letters in or a double straight quotation mark (“). For example, 5 inches is written as 5 in or 5”. 

Description

Inch is one of the smaller units of length measurement in the British imperial and the United States customary system of measurement. This estimation is thought to have derived from the width of the human thumb. The word ‘inch’ was derived from the Roman word "uncia" (twelfth).

In the past, there have been multiple standards regarding the exact measurement of an inch. However, with the adoption of the international yard during the 1950s and 1960s, the inch has been based on the metric system and defined as exactly 25.4 mm.

So it is quite easy to convert centimeter to inch or in to cm. According to the international scales, there are 2.54 centimeters in an inch. So inversely, an inch is equivalent to 1/2.54 centimeters.

For inch to foot conversion, note that one foot is equal to 12 inches. So, while doing ft to in conversion just divide the inch digits by 12 since an inch is equivalent to 1/12 feet. For in to yard conversion, an inch is equivalent to 1/36 yard.

History

Inch was used in the Textus Roffensis in 1120. It is the only surviving manuscript from the Laws of Æthelberht (which dates to the early 7th century). It is the earliest known reference to the inch in England. 

King Edward II of England proclaimed in 1324 that one inch was equivalent to three barley grains put end to end lengthwise. But as the barley grains' size could not be fixed, there was a possibility of having error in standardizing inch by this defintion. Actually before the establishment of the international yard and pound, numerous definitions were used for inch.

In 1912, US and UK followed different definitions of inch measurement. Carl Edvard Johansson then reached a compromise. He produced gauge blocks with a nominal size of 25.4 mm that were accurate to within a few parts per million of both official standards. Because of the popularity of Johansson's blocks, several countries began using 25.4 mm as the inch between 1930 and 1964. It became known as the industrial inch. And this has since become the new official measurement of the inch. 

Use

Inch is mostly used in countries following the FPS (foot-pound-second) system of units. It is sometimes used for measuring small dimensions such as mobile display or electronic parts.