Square footage of a room is a measurement of area, so calculating it requires the length of the room and the width. By placing a tape measure at the edge of one wall and measuring a perfectly straight line to the opposite wall, a measurement can be obtained.
After measuring the length and width of the room, multiplying the two numbers yields the square footage. For example, a room measuring 10 feet by 15 feet would be 150 square feet in area. This helps when choosing how much tile or carpeting to buy when redecorating the room.
Not all rooms are shaped like a simple quadrilateral. There may be smaller sections, triangular or even circular rooms. By dividing irregularly shaped rooms into segments and adding the square footages, accurate measurements can still be obtained. To start, divide the room into its component shapes, starting with the largest quadrilateral. To find the area of a triangle, multiply the base by the height and divide the result by 2. For a circle, multiply pi (approximately 3.14) by the square of the radius. For an elliptical shape, multiply pi by the long and short axes. After finding the areas of the component shapes, add them all together.