Measure the length of the table using the tape measure. Measure to the nearest quarter-inch for accuracy and keep the math simple.
Measure the width of the table, again to the nearest quarter-inch.
Convert the length and width from inches to decimal readings by dividing the inches portion of each measurement by 12. For example, if the table is 3 feet 4 1/4 inches long, the inches at 4.25 will be divided by 12, giving a table length of 3.354 feet.
Multiply the decimal length times the decimal width. The result is the square foot area of the table.
Measure the diameter of the table using the tape measure. The diameter is the length across the table directly through the center. Divide the diameter in half. Half the diameter is called the radius of a circle.
Convert the radius measurement to decimal by dividing the inches portion of the measurement by 12. For example, a table with a radius of 3 feet 9 inches has a decimal radius of 3.75 feet.
Calculate the area of the circular table using the formula for the area of a circle: Area equals pi times the radius squared. Pi is a constant value of 3.1416. To square is to multiply by the number by itself. In the example, the round-table calculation will be 3.1416 x 3.75 x 3.75 equals 44.18 square feet, rounded to two places.