To dice is to cut a fruit or vegetable into small squares or cubes.
To dice, you wash, then peel the fruit or vegetable, then cut it into sticks whose width is the size of the dice you want to end up with, then stack those sticks three or four high then slice off the cubes in the width you want them to be.
Different sizes of dicing are called upon for different uses.
- Large dice = ¾” (20 mm) cubed
- Medium dice = ½” (13 mm) cubed
- Small dice = ¼” ( 6 mm) cubed
- Brunoise = 1/8” (3 mm) cubed
- Fine Brunoise = 1/16” (1.5 mm) cubed
The problem is that many casual recipe writers will just say “dice” without specifying what size they are after. If the measurements are also given in volume, such as “2 cups diced celery”, that can result in various readers of that recipe ending up with quite different amounts of celery in weight in the end.
That generally doesn’t matter in cooking, but could matter when using a tested home-canning recipe where precision can matter.
That being said, even if you did give a home cook precise dice sizes, you can’t be sure they would follow them accurately.