Mils

Mils is the plural form of mil, a term used in two different measurement contexts. In general writing about measurements, mils may refer to either a unit of length or an angular unit, depending on the field of application. The term is also encountered in consumer and industrial contexts where precise thickness or coating measurements are important.

As a unit of length, a mil equals one thousandth of an inch. This thickness unit is commonly used in manufacturing and engineering to specify film, coating, insulation, or wire thickness. One mil is 0.001 inches, or about 0.0254 millimeters. The mil used in this sense should not be confused with metric units such as millimeters, even though both express small dimensions.

As an angular unit, mil (often called milliradian in full) is defined as one thousandth of a radian. In this sense, 1 mil ≈ 0.001 radians ≈ 0.0573 degrees. Angular mils are widely used in firearms, optics, and surveying to describe elevations and aiming references. In the NATO mil system, a target subtending 1 mil at a given distance corresponds to a simple proportional relationship: about 10 centimeters at 100 meters, about 1 meter at 1,000 meters, and so on. Reticles and ballistic calculations frequently employ mils for ranging and holdovers, sometimes in competition with the alternative unit of angle, the minute of angle (MOA).

Because mil has distinct meanings in length and angle, context is essential to determine which definition is intended. Both senses share the same name but apply to different measurement domains.