Obtain a frame that is larger than the piece you wish to display. The frame should be large enough to house the artwork and the mat. If you want a 1-inch mat, the frame should be 1 inch larger than your art on each side.
Calculate the border size before you begin cutting. Measure the artwork horizontally and vertically. This will give you the size calculation for the interior cutout of the mat. For a 1-inch mat, add an inch to each calculation for the exterior of the mat. For example, an 8-by-10 photo would have an 8-by-10 interior cutout and a 9-by-11 exterior border.
Use a pencil and ruler to mark the exterior and interior borders for your mat. If you want a 3-inch border, mark the exterior lines 3 inches larger than the necessary interior size. Then measure 3 inches from the edge of your exterior lines to mark the borders of the interior. Draw the interior based on these marks. Slowly cut the mat along these marks. If you cut too quickly, you may allow the cutter to slide too far and end up with a damaged mat or a larger cut than you anticipated.
To cut offset corners, mark your mat as usual. Create a small 1/4-inch square at each corner of the interior by measuring along the interior lines and marking the squares. The cuts will give you small square corners in the interior that will lend a decorative edge to the mat.
Sometimes you may have an oval or circular frame. To cut ovals and circles properly, you need a mat cutter designed for these shapes. This cutter works a lot like the compass you may have used for drawing circles in math class.
To use an oval and circle mat cutter, place your left hand on the center of the cutter as your positioning hand to hold the mat and the cutter in place. Use your right hand to rotate the cutting arm. Your left hand will be in the way of the cutting arm as it rotates, but do not pick up that hand. This could displace the cutter and result in a crooked cut.
Instead, keep your hand in position and rotate the cutting arm clockwise until it will not comfortably go any farther. Then rotate the cutting arm counterclockwise back to the original position. Rotate the mat counterclockwise until the cut part meets with the cutting arm, and then continue to rotate the arm. Continue this process until the entire mat is cut.