90mm

90 millimeters (90 mm) is a unit of length in the metric system. It equals 0.09 meters, which is 9 centimeters or about 3.543 inches. The millimeter is one thousandth of a meter and is commonly used for measuring small distances, thicknesses, and dimensions in science, engineering, and everyday life.

In contexts such as firearms and artillery, 90 mm is used as a bore diameter designation, referring to weapons whose bore measures 90 millimeters. Calibers of this size have been employed by several countries for anti-tank and anti-aircraft guns and related weapons, especially during the mid-20th century and into the Cold War.

Examples of such uses include 90 mm caliber guns developed for defense roles, including anti-tank cannons and anti-aircraft guns. The 90 mm designation also appears in some tank and self-propelled gun designs and in naval artillery in various periods.

In photography and optics, 90 mm is a common focal length for telephoto lenses, offering moderate magnification for portrait and wildlife work. While the prominence of 90 mm varies by field, the designation consistently refers to a dimension or spec measured in millimeters and is part of the broader system of metric units used worldwide.