You can find two types of dimensions for a standard rectangle. Length, width and height for three-dimensional objects can be found using a tape measure. Volume or surface area have to be found with a mathematical equation, using the information gathered with the tape measure.
Find the length of the rectangle by measuring one of the longer sides. Find the width by measuring a shorter side. If the rectangle is a three-dimensional object, find the height by measuring from the bottom of the rectangle to the top. It doesn't matter what unit of measurement you use to find this information (for example, centimeters or inches), but find all three measurements using the same unit.
Add the measurements of all four sides to find the perimeter. For example, if the longer sides measure 5 inches and the shorter sides measure 2 inches, the perimeter is 14 inches (5 + 5 + 2 + 2).
Find the area by multiplying the length and width. For example, a 5-inch-by-2-inch rectangle would have an area of 10 square inches.
Find the volume of your rectangle by multiplying the area by the height. For example, if the rectangle's area is 10 square inches and its height is 5 inches, the volume is 50 cubic inches.