The standard depth for a Formica countertop is 25 1/4 inches. These countertops are designed to fit standard cabinets, which are 24 1/4 inches deep. The 25 1/4 inch countertops typically include a nosing on the outer edge that gives the counters a slightly more decorative appeal. According to the Family Handyman website, cabinets that vary more than 1/4 inch from the standard 24 1/4 size require a custom-sized countertop.
Preparing to put in laminate countertops requires that you ensure that your walls are straight and your corners are square. The typical Formica counter is designed so that you can shave off up to 1/4 inch from the edges, if necessary, to accommodate any problems with the walls or corners. Beyond that, it will be necessary to order countertops that are deeper than normal. This will allow you to shave off what you do not need to account for any irregularities.
Formica countertops vary from natural stone or synthetic countertops, like Corian, in their basic composition. The typical Formica countertop consists of a 3/4-inch piece of plywood or particle board substrate, covered by a thin sheet of decorative laminate that is generally composed of some type of plastic material.
Installation of Formica counters is fairly basic and simple compared with other types of countertops. Once the old counter has been removed and the new countertop has been prepared for the existing space, you can simply place it so that it rests upon the top edges of the existing counters. Drive wood screws up through the cabinet base to secure the counter in place. You can also use wood glue before you situate the countertop for some additional adhesion.