Measure the bottom of the cabinet with a measuring tape. Measure the length of both the front and side of the base cabinet. Your toe kick will be smaller than this dimension.
Set a table saw for a 4-inch cut. Run a sheet of ¾-inch medium density fiberboard through the table saw. Four inches is the height of the toe kick.
Cut two pieces of the 4-inch MDF to the make the front and back of the toe kick. Use a circular saw to make the cuts. The boards should be cut 6 inches shorter than the length of the front of the base cabinet. This will leave a 3-inch recession on each side of the cabinet when the toe kick is installed.
Cut two pieces of 4-inch MDF for the sides and three pieces for the cross supports. The boards should be cut 5½ inches shorter than the length of the side of the cabinet. This will produce a 4-inch toe kick recess in the front of the cabinet.
Put a front and side board on the table. Insert 1¼-inch staples in a staple gun. Place the ends of the two boards together. The boards should be flush on the top and sides, with the end of the side board butting into the end of the front board.
Hold the boards firmly together and shoot a staple through the end of the front board into the side board. You should place a staple near the top of the end board to secure the board in place. Shoot another staple through the front board near the bottom of the side board. Add another staple in the middle of the two others. Repeat this procedure for the other front and side boards. Staple all four corners.
Place a cross support in the top right side of the toe kick. The board should be flush with the top of the toe kick and flush with both the front, back and side boards. Shoot staples through the front of the toe kick into the edge of the cross support. Put a staple near each end of the cross support and one in the middle of the cross support. Shoot several evenly spaced staples along the top edge of the side board into the side edge of the cross support to firmly connect the boards.
Insert the last cross support in the middle of the top of the toe kick. Staple the cross support in using the same procedure used for the side boards.