Diced vegetables look appealing in a finished dish, but beyond aesthetics, a proper dice serves a practical purpose: the evenly sized pieces cook at the same rate. You can dice any vegetable, including onions, potatoes, peppers, carrots and celery.
Wash the vegetable under running water, scrubbing lightly with a vegetable brush if necessary. Trim off the leaves and peel the vegetable if needed. Cut peppers, tomatoes and other seed-filled vegetables in half and scoop out the seeds before you begin to dice.
Cut large vegetables, such as onions, in half. Cut vegetables such as carrots, which don't have a uniform shape, into pieces of similar size.
Place the vegetable flat on the cutting board. Cut the vegetable into horizontal strips of equal width. Make the strips ¾-inch wide for a large dice, ½-inch wide for a medium dice or ¼-inch wide for a small dice.
Hold your knife perpendicularly to the strips and cut the vegetables into cubes. Space the cuts evenly so you have large, medium or small cubes of equal size.