Ordering

• Prefab countertops usually come in a standard depth of 26 inches, to accommodate standard floor cabinets while leaving a small overhang at the front without requiring cutting. The length of the countertops come in varying incremental sizes, and may not be available in the exact length you need, meaning you'll have to cut one side. When ordering, get the closest available length that's at least 3/4 inch longer than the length of your combined floor cabinets.
  
  

Preparation

• If you're replacing an existing countertop, wait until the new one arrives before taking out the old one. Remove the old one by cutting away any caulk between the countertop and the walls, then unscrew it from the wood or metal brackets below and lift it off. Make sure your cabinets are level before installing the new countertop--level them with shims at the floor, if necessary.
  
  

Cutting

• If you have to trim the length of your countertop, it's always best to cut a side that goes against a wall, if possible. That way, you don't have to finish the edge. Cut it with a circular saw, using a fine-toothed carbide blade. To get a straight cut, clamp a 1-by-3 board parallel to your mark, as far over as the width of your saw's blade plate, so you can butt the plate up against the wood and use it as a guide. Lay a piece of masking tape over your marked line, then re-draw the line on top of it and make the cut right over the masking tape. This will prevent the laminate from chipping. (If you have to cut out a center area for a sink, use a jigsaw, but follow the same procedure, setting up a saw guide and taping the lines.)
  
  

Mounting and Finishing

• Mount the countertop from underneath, putting wood screws up through the triangular wood brackets attached to the cabinets. In some designs, the countertop will install with metal brackets. Once it's in, caulk between the countertop and the wall wherever they meet. If you had to cut an end that isn't against a wall, laminate the end using a strip of the same laminate. Use a jigsaw to cut the strip a little bigger than the edge, secure it with contact cement, then trim off the overhanging laminate using a router fitted with a laminate bit.