- 1). Determine the measurements of the surface that the countertop will be installed with a measuring tape. Measure the back edge along the wall, which will provide the correct length for the longest section of the countertop. Mark the measurements on the surface with a pencil.
- 2). Transfer the measurements to the countertop with a pencil. Turn the cabinet over and draw the marks on the underside with a pencil and a straightedge.
- 3). Hold a carpenter's square along the lines you drew on the underside of the countertop.The square will help you create a 45-degree angle. Mark the angle with a pencil. You will use this line to create the cut.
- 4). Make a 45-degree angle cut in the countertop. Cut with the countertop flipped upside down and saw along the line you drew.
- 5). Repeat this method with the second section of countertop. When the two pieces fit together, the two 45-degree angles will make a 90-degree corner.
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