The inch is a unit of length used within the imperial and US customary systems of measurement. Defined as a standardized measure, it is a subsystem of the foot, which itself is derived historically from the human body but is currently maintained as a precise mathematical constant for scientific and engineering applications. The use of inches allows for the standardized quantification of physical dimensions, facilitating consistency in fields such as carpentry, mechanical engineering, and material science. Because it is defined relative to other standardized units, the inch allows for the calculation of area, volume, and force across various disciplines of physical science.