A standard under-counter dishwasher opening is 24 inches wide. The exact measurements of openings and dishwashers vary slightly. Measuring before shopping prevents problems during installation.
Standard built-in dishwashers are 24 inches deep, 24 inches wide and 35 inches tall, with height-adjustable feet. Tall-tub dishwashers fit into the same size opening but have a larger interior chamber. Two-drawer dishwashers are shorter, but they fit into standard-size openings because the appliances' heights are adjustable.
The distance from floor to counter is not a reliable measurement of the height of the opening. Floors installed after the existing cabinet and appliance installation can be laid on top of pre-existing flooring, making the visible floor higher than the floor present under the installed dishwasher.