microinches

Microinch is a unit of length in the United States customary system equal to one millionth of an inch. It is commonly abbreviated as μin or µin and may appear in full as microinch. One microinch is 1 × 10^-6 inch.

Conversion to metric units: 1 µin equals 25.4 nanometers, and 0.0254 micrometers. This makes microinches useful for expressing very small dimensions when working with imperial units, particularly in contexts where measurements are tied to inch-based tooling and specifications.

Usage and context: Microinches are frequently used in engineering and manufacturing to specify tolerances, film thickness, and surface finishes. In precision machining, tolerances may be given in microinches (for example, ±5 µin). Surface roughness and coating thickness are also reported in microinches in some industries, with common roughness values ranging from tens to hundreds of microinches (Ra). The unit remains prevalent in many legacy US standards and in sectors such as tooling, electronics, and some aerospace applications.

Status and alternatives: The microinch is not an SI unit and is largely replaced by metric units in international contexts. In modern documentation, thickness, roughness, and tolerances are increasingly expressed in micrometers or nanometers. Nevertheless, microinches persist in historical data and in particular US-based specifications.

Measurement considerations: Instruments that read inches, such as micrometers or profilometers, often report values in microinches when aligned to inch-based standards. Conversion to metric units should be performed carefully to maintain precision.