How big is an inch in diameter

How to convert inches immediately.

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If you are very easy Inches to cm want to convert, play around with the slider or enter your values ​​(as a whole number or decimal number) in the fields provided. Use our tables for fractions. If the slider can no longer be moved (can happen), simply click in the menu on the converter item (= start page).


Inch value in centimeter value
Centimeter value in inch value


Here is a short video on how to convert inches to cm.


Do you want to know more about the unit of measurement?

The inch length measure is hardly used in Germany any more. However, there are some size specifications in which this unit is still used, for example when specifying the screen diagonal for TV sets, computers or notebooks or the diameter of car and bicycle rims. Therefore, it should prove useful if you know how to calculate cm from inches or vice versa. After all, you don't always have an inch converter at hand.

1. story

The name comes from the Middle High German word "Zol", which means something like "cut piece of wood". In ancient times, pieces of wood cut to a specific size were used to measure lengths. Your own body was used as a guide. Therefore, measurements such as a hand's breadth, a foot or a cubit were quite different. The same was of course true of the inch, which was measured according to the width of the thumb.

The English equivalent of the inch, the inch, is first found in the laws of King Æthelberht of Kent, who ruled in the early 7th century. Inch comes from the Latin uncia (twelfth) and in this case meant the twelfth of a foot. King Henry I of England set this unit of measurement to be the width of his thumb in 1101. In 1234 Edward II of England changed the inch from a width to a length and determined its dimensions to be three grains of barley placed one behind the other. Since these are not of the same size, there were still differences.

Even in the 20th century there were different definitions around the world, even if the deviation was less than 0.001 percent. The British Standards Institution defined the unit of measurement in 1930 to be exactly 25.4 millimeters. In 1933 the American Standards Association followed suit. This definition was legally recognized by Canada in 1951. In 1959, the USA and the countries of the United Kingdom of Great Britain and Northern Ireland signed an agreement of consent for the definition of the uniformly defined 25.4 millimeters.

While in Germany since the introduction of the metric system in 1872 cm has been used instead of inches, the identical inch is the usual measure of length in the USA. The Americans, like the states of Liberia and Myanmar, still adhere to the Anglo-American system of measurement.

2. Definition

The unit of measurement has been internationally recognized since 1959 and is defined as 25.4 millimeters in length. So 1 centimeter is 0.39370 inches.

The corresponding square measure is the square inch, which corresponds to 6.4516 square centimeters.

3. Spellings

Both "in" (according to ISO 31-1 Annex A) and the customs symbol ″, which is the same as the second symbol, serve as the standard symbol.

1 in = 1 ″
= 1000 Thou (Thousands on an Inch) = 1/12 ft (Feet) = 1/36 yd (Yard) = 25.4 mm

4. Conversion

You can easily calculate cm from inches by multiplying the starting value by 2.54. Conversely, you divide the centimeters by 2.54 to get the inch value.

Centimeters = inches * 2.54

Inches = centimeters / 2.54

As a donkey bridge, it is advisable to memorize the three digits in a certain context, for example in a simple sentence like:

2 cats eat 5 mice in 4 days.

Of course, the conversion is particularly quick and accurate with our inch converter. Alternatively, there are some conversion tables available.

5. Use

Although the measured variable is largely out of use in Germany, you can still discover it in many areas. The “folding rule”, for example, is well known, even if it uses cm as a unit of measurement instead of inches. The official name is "folding rule", but hardly anyone uses this term. There are also numerous other examples.

Customs information in clothing

You have surely come across inches when buying trousers. Particularly for jeans, specifications such as W 34 ″ / L 36 ″ (W = English: waist = waist size, L = English: length = length) are quite common. In international trade, this unit is also widely used when specifying heel heights for women's shoes, especially high heels, and the thickness of the plateaus for platform shoes.


Customs information for electronic devices

In this country, the customs value is primarily known as a measure of the screen size of televisions, computers and laptops (40 ″ = 102 cm). The display size of smartphones, tablets, e-book readers and navigation devices is also given in this otherwise rather uncommon unit. The same goes for the size of hard drives and computer optical drives. The floppy disks, which had since gone out of fashion, were also provided with customs information.

In the field of event technology, this unit of measurement is used for threads for microphone stands and for lamp spigots. Loudspeaker diameters are also given in inches rather than centimeters. In the case of sound carriers, the inch size has also prevailed, even if this is very imprecise information that differs significantly from the real size. The diameter of 7 ″ singles is actually only 175 instead of 178 mm, with 10 ″ EPs it is only 250 instead of 254 mm and with 12 ″ LPs only 300 instead of 305 mm. It is similar with the tonearms of turntables. The tonearm lengths are, for example, 9 ″, 10 ″ or 12 ″.

The unit is just as decisive for the grid dimension on printed circuit boards as well as for ribbon cables, connectors, IC housings and prototype boards as it is for the wafer diameter for semiconductors. In addition, the inch serves as the basic unit for calculating the AWG (American Wire Gauge) coding for the wire diameter in electrical cables and as a measure for wire cross-sections in small-signal applications. It is also used with numerous standards of US origin, e.g. B. the Universal Serial Bus (USB).

Customs information for optical devices and photography

You can also find customs values ​​for the diameter of eyepieces and receptacles, photo cameras and telescopes as well as the openings of telescopes (4 ″ = 10 cm). The diameter of the tripod thread of photographic cameras is usually 1/4 ″. With medium format cameras it is often 3/8 ″. Are you interested in old telescopes? The focal lengths of the earliest models were also given in inches, while feet were later used.

Customs information in vehicle construction

In the case of bicycle rims and tubes, you will usually search in vain for centimeters. The same applies in part to frame sizes, the tube diameter on the steering column, the stem and the handlebars.

You will also find inch specifications for car rims, hubcaps and the tire width of diagonal tires. On the other hand, you do not need an inch size converter for radial tires (radial tires), as the width is specified in millimeters.

Customs information in sports and sports equipment

Perhaps you have already noticed the size specifications for skateboards. Here, too, you will find inch sizes for the decks as well as for axles, rollers and some other components. For surfboards it is also common to indicate the size in ″. This unit is also typical for archery, for example when specifying lengths for bows and arrows or when measuring the distance between the bowstring and the fulcrum. For firearms and air guns, the inch is used for the caliber information.

Would you like to buy a tennis racket? Then an inch converter, with which you can convert inches to cm, can also be useful. For example, there is a handle size L 3 with 4 3/8 "(111 mm). Customs values ​​are also used for golf club fitting, and in the 110 m hurdles the men jump a height of 42 ″ (106.68 cm).

Customs information in tool and mechanical engineering

Inch sizes are also used for the Whitworth pipe threads commonly used in the gas, hydraulic and pneumatic sectors. However, the specifications for the thread sizes of the tapered Whitworth pipe threads do not correspond to the actual values. With a 1 ″ thread, for example, the outer diameter is 3.325 centimeters instead of 2.54 centimeters. There are historical reasons for this. Originally, the dimensions referred to the inside diameter of the cast iron pipes used at the time. In the meantime, however, the pipe wall thickness has decreased due to better materials and manufacturing processes. So that the new pipes also fit into existing installations, the outer diameter was retained and the inner diameter increased. The size specifications remained unchanged and today neither correspond to the internal nor the external dimensions. Even the best inch converter won't help you.

For threads of non-uniformly standardized gas-specific valve connections and protective caps of pressurized gas cylinders, inch specifications are just as normal as for screw connections in the gas, hydraulic and pneumatic area (e.g. pressure gauges). The same applies to threads for fastening screws (especially in the USA) and to computer elements such as connector fixing screws (e.g. on the D-Sub).

Drives for square socket wrenches (ratchets, ratchets) are available, for example, in sizes of 1/2 "or 1/4", drives for hexagonal bits in sizes of 1/4 ", 5/32" or 5/16 ". Inch dimensions also apply as the pitch of drive chains in machines or for saw chains.

Customs information in printing technology

Customs values ​​are also used in many areas of printing technology, for example for paper sizes, line and font heights and character spacing. One DTP point is 1/72 ″. This corresponds to about 0.3528 mm. The standard tablature on typewriters jumps in 1/10 ″ steps. The standard line feed for continuous paper follows a 1/8 ″ grid.

Customs information in other areas

The winding cores of adhesive tapes often have a smooth inch diameter, for example Gaffa tape 3 ″ and packing tape 5 ″. With adhesive tape widths, a value of 3/4 ″ often appears. You will find the same dimension if you measure the distance between the contact pins and the Euro plugs.

Do you play a musical instrument? Here, inch specifications apply to the most varied of lengths, such as the neck length, the frame height and the body width of stringed instruments, the dimensions of the mouthpieces on wind instruments or the head diameter of percussion instruments.

Use of inch size in trade

Since we use the metric system, the use of customs information in trade is sometimes controversial. For example, opponents who would prefer centimeter values ​​see a violation of the law of units and time in the dimensions for screens, unless the respective sizes in centimeters are clearly highlighted. Proponents, on the other hand, see the customs designations only as product classes for which this law would not apply.