In order to evaluate a dishwasher's performance, we use them to wash dishes, flatware, and glasses--113 items in all--in a repeatable, reproducible manner, controlling all external variables.

Dishes are soiled with regular ingredients in precise ways (at certain angles and in certain amounts) and are allowed to sit overnight (below, left). The soiled dishes are then washed in the tested models, using the same type and amount of detergent and using prefiltered water at the same temperature of 120° F. Each model is tested multiple times. We judge wash performance by inspecting each item in the dishwasher for signs of visible soil, water spotting, and invisible grit.

Besides testing wash performance, we also look at the model's components (below, right), including the filter at the bottom of a dishwasher, which is used to remove food particles from the recirculating washwater, and the food-grinder feature, which is used to chop large chunks of food into smaller particles that can be flushed down the drain. Dishwashers with a better filter and food grinder are able to minimize visible soil and invisible grit.