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.
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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.