So what is the size difference between the full sized and 18 inch dishwashers? They are a full six inches smaller compared to the standard full-sized 24 inch. They go by another name that you might know, slimline. These 18 inches are the ideal dishwashing machines for folks which don’t have a large kitchen. 18 inch dishwashers can be grouped into two classes; 1) portable with casting wheels 2) fixed, where they’re placed on the countertop, or built-in.