Step 1 : Divide your countertops into sections

Step 2 : Add the total inches (example shown below 96+62+48+60=266 inches)

Step 3 : Use the following calculator to get the total of Length (inch) x  Width (The width of most cabinets are usually 25.5 inches)

Step 4 : For round surfaces or islands use the following calculator to calculate the area of the section.

Step 5 : Add all the area calculations and divide it by 144 to convert square inch into square foot.

Here is an example:

From the example shown above we will add all the lengths 96+62+48+60=266 inches
Now we multiply 266 inch by 25.5 inch to get our surface area which is equal to 6783 square inch.
Then we divide 6783 by 144 to convert square inches into square feet which is equal to 47.10 square feet

Some things to remember!

Kitchen: Base cabinets are 24 inch, so stone is cut 25.5inch
Vanity : Base cabinets are 21inch, so stone is cut 22.5 inch
Mini Granite Back-Splash: Input length in inches x height (usually 4 inch)