Place a stool or chair next to the counter and measure how many inches the counter will extend past where it currently is. Then measure how far it currently extends past the cabinet. Add these two measurements together. This determines how much extra width must be added to create a breakfast bar.
Cut a piece of wood the exact width required to extend the counter with a circular or wood saw.
Sand the wood down with medium-grit sandpaper. Vacuum all excess grit from the wood.
Apply stain to the wood by putting some stain on a cloth and rubbing it on the wood. Select a stain color that matches your cabinets or compliments the countertop. Allow it to dry. Apply a second coat if necessary. Let dry.
Open the folding shelf bracket. Butt the bracket's shortest side flat against the cabinet, and 5 inches from where the side end of the counter extension will be.
Mark the screw holes with a pencil. Remove the bracket.
Predrill holes into the screw marks using an electric drill. Screw toggle bolts with your hands into the predrilled holes.
Replace the bracket and secure it in place with its screws. Repeat the process to secure any additional brackets. Install a folding shelf bracket every 1 to 2 feet.
Place a level over the installed brackets to ensure they are even. If not, unscrew and adjust them accordingly.
Fully extend the folding shelf brackets. Place wood on top of the extended brackets. Make sure the wood butts up against the end of the countertop, leaving about a 1/4-inch gap between the two, and is centered.
Get underneath the extended brackets and mark screw holes through the bracket with a pencil.
Remove the wood and place it flat on a work surface. Predrill holes through each screw hole mark. Twist a toggle bolt into each hole.
Reposition the wood back over the extended brackets. Get underneath and make sure the predrilled holes are aligned with the screw holes in the bracket. Tighten the bracket to the underside with screws.
Fold down and unfold the newly extended breakfast bar to make sure the brackets are operating correctly.