of firewood. The square is used to mean 100 square feet in construction. Heat flux in the U.S. is measured in langleys. Other names for U.S. customary units The United States Code refers to these units as "traditional systems of weights and measures". Other common ways of referring to the system are: customary, standard, English, or imperial (which refers to the post-1824 reform measures used throughout the British Empire & Commonwealth countries). Another term is the foot–pound–second (FPS) system, as opposed to centimeter–gram–second (CGS) and meter–kilogram–second (MKS) systems. Tools and fasteners with sizes measured in inches are sometimes called "SAE bolts" or "SAE wrenches" to differentiate them from their metric counterparts. The Society of Automotive Engineers (SAE) originally developed fasteners standards using U.S. units for the U.S. auto industry; the organization now uses metric units. See also Board foot Conversion of units History of measurement and units of measurement Plan for Establishing Uniformity in the Coinage, Weights, and Measures of the United States (1790) Mars Climate Orbiter, which failed due to a measurement-units-related software bug Standard cubic foot References External links Rowlett's Dictionary of Units of Measurement (archived) Imperial units Systems of units