archCalc

archCalc is a mixed unit decimal and fraction construction calculator. It allows one to enter dimensions in standard english and metric units of measurement, perform basic calculations, convert between units, keep track of a series of operations, and easily solve for a leg or slope of a right triangle.
archCalc works as a standalone calculator or in conjunction with other programs, calculating stair risers in CAD software, or aiding in takeoffs with a spreadsheet.

archCalc floats above applications allowing one to work with it as if it were a part of the active application.