An inch is the name of a unit of length in a number of different systems, including Imperial units, and United States customary units. There are 36 inches in a yard and 12 inches in a foot. The inch is usually the universal unit of measurement in the United States, and is widely used in the United Kingdom, and Canada, despite the introduction of metric to the latter two in the 1960s and 1970s, respectively. The inch is still commonly used informally, although somewhat less, in other Commonwealth nations such as Australia; an example being the long standing tradition of measuring the height of newborn children in inches rather than centimetres. The international inch is defined to be equal to 25.4 millimeters.

››Definition: Radian

In mathematics and physics, the radian is a unit of angle measure. It is the SI derived unit of angle. It is defined as the angle subtended at the center of a circle by an arc of circumference equal in length to the radius of the circle. Angle measures in radians are often given without any explicit unit. When a unit is given, sometimes the abbreviation rad is used, sometimes the symbol c (for "circular").

››Metric conversions and more

ConvertUnits.com provides an online
conversion calculator for all types of measurement units.
You can find metric conversion tables for SI units, as well
as English units, currency, and other data. Type in unit
symbols, abbreviations, or full names for units of length,
area, mass, pressure, and other types. Examples include mm,
inch, 100 kg, US fluid ounce, 6'3", 10 stone 4, cubic cm,
metres squared, grams, moles, feet per second, and many more!