How to Calculate the Amount of Granite Needed for Countertops
Granite for countertops is sold in terms of square footage. This means that determining how much granite you need for your countertop is simply a matter of finding out the overall square footage of your countertop area.
Things You Will Need
 Tape measure
 Pen and paper
Because granite comes in slabs, there is the possibility that the measurements of your countertop will not exactly match the available sizes of granite slab. This should not be a problem, however, since most granite countertop providers will only charge you for the section of the slab that you use.

Measure the length of your countertop along the wall in inches. This measurement should include a one inch overhang for any edge of the countertop that is not against a wall. If your counter is broken up into sections due to the presence of a sink or oven, subtract this unoccupied space from the overall length.

Measure the width of your countertop. This measurement should begin along the wall and extend outward to the front of the countertop.

Multiply the length of the countertop by the width of the countertop. The resulting number is the area of your countertop expressed in square inches.

Measure the height of any backsplashes. The measurement should reach from the surface of the countertop to the top of the backsplash.

Multiply the height of the backsplash by the length of the countertop. The resulting number is the area of your backsplash.

Add the area of your countertop to the area of your backsplash. The resulting number is the total amount of granite you need expressed in square inches.

Convert the results to square feet. To do this, divide the number of square inches by 144.
Tip
The average countertop width is 26 inches.
Things You Will Need
 Tape measure
 Pen and paper
Tip
 The average countertop width is 26 inches.