48mm

48mm denotes a measurement of 48 millimeters, equal to 4.8 centimeters or 0.048 meters. It is used as a dimension in a range of products and specifications across different fields.

In photography and cinematography, 48mm refers to a focal length. On a full-frame 35mm sensor, 48mm is near normal in perspective, producing an angle of view close to that of the human eye. On cameras with smaller sensors, such as APS-C or Micro Four Thirds, a 48mm lens has a longer effective focal length due to crop factor (for example, about 72mm on APS-C with a 1.5x crop), resulting in a tighter field of view and more background separation.

In wristwatches, 48mm is a common case diameter for larger, rugged models, particularly dive and professional watches. The measurement is taken across the widest part of the case, normally excluding protruding crowns. Watch sizes have trended upward in recent decades, with 48mm community-accepted as a large-format option for masculine and sport-oriented designs.

In optics and camera gear, 48mm also appears as a front-diameter specification, indicating the size of filters or attaches that can be mounted on lenses with a 48mm outer diameter. Users should verify thread pitch and compatibility, as front diameter does not by itself guarantee fit for all accessories.

Other engineering contexts use 48 mm as a standard dimension for components such as tubes, bushings, or fittings, where precise metric sizing supports interoperability and replacement parts.