The area of a square or rectangular room can be calculated in square feet by measuring the length and width of the room in feet and multiplying the two numbers. The calculation of the area of a room depends on its shape, according to Math Is Fun.
For a triangular room, measure the floor and height in feet. Multiply these together and divide the result by two; the result is the area of the triangular room. To find the area of a circular room, measure the number of feet from a point on the wall to the center of the room to determine the radius. Multiply the radius by 3.14, and the result is the square footage of the room. For a half-circle room, divide the total area by two. Using these methods or a combination of them, the area of a room can be determined no matter its shape.