Rectangular Steel Surface

• 1). Measure the length and width, in inches, of the rectangular steel sheet. For example, the length might be 135 inches while the width is 50 inches.
  
  
• 2). Multiply the length by the width to obtain the area of the steel in square inches. Now, for the example, you have 135 inches times 50 inches, or an area of 6,750 square inches.
  
  
• 3). Divide the area by 144 to change to square feet, since 144 square inches equals one square foot. Completing the example, you have 6,750 square inches divided by 144 square inches per square foot, or a steel area of 46.9 square feet.
  
  

Circular Steel Surface

• 1). Measure the circumference, or total distance around the circular steel sheet, in inches. For example, the circumference might be 325 inches.
  
  
• 2). Divide the circumference by two times pi (3.14), or 6.28, to arrive at the radius in inches. Performing this step, for the example, leads to 325 inches divided by 6.28, or a radius of 51.8 inches.
  
  
• 3). Multiply the pi by the square of the radius to arrive at the area of the steel in square inches. Square the radius by multiplying it by itself once. This step, for the example, yields 3.14 times 51.8 inches times 51.8 inches, or an area of 8,425.4 square inches.
  
  
• 4). Convert the area to square feet by dividing by 1,728. Completing the exercise leads to 8,425.4 square inches divided by 1,728 square inches per square foot, or a circular steel area of 4.9 square feet.