Estimate and Calculate the Perimeter of Rectangles . Perimeter is an application of length so estimating the perimeter of rectangles requires knowledge of length and a familiarity with units of length. Teaching students about perimeter often has a focus on the use of formulas. . Formulas that are taught as something to be remembered will often get muddled together when students try to apply them, especially after a period of time when they haven’t been accessed or used. . Understanding why a for