A rectangle is a geometric shape that is a type of quadrilateral. This four-sided polygon has four angles, with each equaling 90 degrees. You may be required to find the area or width of a rectangle as an assignment in a math or geometry class. Knowing how to apply formulas that relate to rectangles also comes in handy if you are performing a real-life task, such as calculating the square footage of a building.
Measure the length of the rectangle with a ruler or tape measure, depending on the size of the shape.
Measure the rectangle's width.
Multiply the length times the width to find the area.
Express your answer in units squared. For instance, if a rectangle is 3 feet in width and 5 feet in length, its area is 15 square feet.
Divide the area by the length if you are given these two figures but not the width. For example, if a rectangle has an area of 20 square feet and a length of 10 feet, divide 20 by 10 to get a width of 2 feet.
Multiply the length times 2 and subtract this figure from the perimeter, if you're given these values. Then divide by 2 to find the width. (In cases where you are given the length and the perimeter.) For instance, if the perimeter is 10 inches and the length is 3 inches, multiply 3 times 2 to get 6. Then subtract 6 from 10 to get 4. Divide 4 by 2 to get a width of 2 inches.
Take the square root of the area to find the width if the rectangle is a square. For instance, if the area of the rectangle (square) is 25 square inches, find the square root of 25. Because 5 times 5 equals 25, 5 is the square root and also the width of the rectangle.