To convert length x width dimensions from millimeters to inches we should multiply each amount by the conversion factor. One millimeter equals 0.0393701 inches, in order to convert 4 x 21 millimeters to inches we have to multiply each amount of millimeters by 0.0393701 to obtain the length and width in inches. In this case to convert 4 x 21 millimeters into inches we should multiply the length which is 4 by 0.0393701 and the width which is 21 by 0.0393701. The result is the following:
4 x 21 millimeters = 0.16 x 0.83 inches
The millimeter (symbol: mm) is a unit of length in the metric system, equal to 1/1000 meter (or 1E-3 meter), which is also an engineering standard unit. 1 inch = 25.4 mm.
An inch (symbol: in) is a unit of length. It is defined as 1⁄12 of a foot, also is 1⁄36 of a yard. Though traditional standards for the exact length of an inch have varied, it is equal to exactly 25.4 mm. The inch is a popularly used customary unit of length in the United States, Canada, and the United Kingdom.
To calculate a millimeter value to the corresponding value in inches, just multiply the quantity in millimeters by 0.0393701 (the conversion factor).
inches = millimeters * 0.0393701
The factor 0.0393701 is the result from the division 1 / 25.4 (inch definition). Therefore, another way would be:
inches = millimeters / 25.4
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