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An inch is a unit of length or distance in a number of systems of measurement, including in the US Customary Units and British Imperial Units. One inch is defined as 1⁄12 of a foot and is therefore 1⁄36 of a yard. According to the modern definition, one inch is equal to 25.4 mm exactly.

The inch is abbreviated as "in" or sometimes as double quotes ("), especially when referring to the size of a screen or display.

Inches are commonly used to measure the length, width, or height of various objects, such as:

The diagonal size of computer or TV screens is often expressed in inches.
The size of furniture, such as tables, desks, or shelves, may be expressed in inches.
Clothing sizes, such as the length of pants or the circumference of a waist, may be expressed in inches.
The size of paper, such as letter or legal size, is often expressed in inches.
The dimensions of construction materials, such as lumber or drywall, are often expressed in inches.

Overall, the inch is a widely used unit of measurement for expressing length or distance in many different contexts and applications in the United States and other countries that use the customary or imperial systems of measurement.

The ångström (A) is a unit of length equal to 10⁻¹⁰ m or 0.1 nm. Its symbol is the Swedish letter Å. The ångström is used in the natural sciences and technology to express very small sizes comparing to that of atoms, and molecules. The ångström is not formally a part of the the International System of Units (SI) and its use is officially discouraged in SI. The closest SI unit, the nanometer (10⁻⁹ m), is recommended for use instead of ångström.