You peel, slice, and chop common ingredients like onions every day. But are you doing it right? Onions (one of the six indispensable aromatics, which also include garlic, leeks, carrots, celery, and shallots) provide the flavor base for countless soups and stews to sauces and salad dressings. Be sure to store onions at cool room temperature and away from light (and not in the refrigerator, where their odors can permeate other foods).

What You'll Learn

Dicing an Onion

1. Cut the Onion in Half: To chop or mince an onion, first halve the onion pole to pole then lay each half cut side down on the cutting board. Lop off the tops of each half and trim the root end, being careful not to remove too much of the onion.

2. Make Several Cuts: Peel the onion, then make several horizontal cuts from one end of the onion half almost to the other, but don’t cut all the way through the root end. The number of cuts will depend on the size of the onion and the desired size of the chop or dice. For minced onion, make closer cuts; for chopped onion, space the cuts further apart.

3. Cut From Pole to Pole: Make several vertical cuts, pole to pole.

4. Slice Across the Cuts: Slice using your knuckles as a guide for the knife while holding the onion with your fingertips. Pull your fingertips in towards your palm, extending the knuckles outward when cutting for more control.

Knife Tip for Dicing Onions

Dicing an onion can be tricky if your chef's knife is dull. We know there is no substitute for regular knife sharpening and honing, but we've found that the tips of our knives—the first 2 inches of the blades, which are usually used to make entry cuts in onions—are often a little dull. We have much better results when we start each horizontal and vertical cut with the middle part of the blade, which is about 4 inches from the tip. This part of the knife is usually sharper.

Does it Matter How You Slice an Onion?

The way in which onions are sliced makes no difference to flavor, but we find it does affect appearance, especially in soups, stews, and braises. Cooked in liquid, onions sliced against the grain (parallel with the root end) turn lifeless and wormy-looking. Sliced with the grain (pole to pole), onions retain more shape and become a more significant component of a dish.

Dicing versus Chopping

In general, the recipe instruction "dice" (or "cube," depending on the recipe writer) denotes more precision than "chop."

That said, "dice" can mean two things: relatively tidy and uniform pieces or painstakingly precise cubes. The latter involves squaring off rounded edges and, hence, a good deal of waste. We almost never require such fussy precision at Cook's Illustrated: When appearance is of considerable importance, we use the less rigid dice, as in diced tomatoes for Fresh Tomato Salsa. We chop on most other occasions (onions for potato salad, celery for stuffing, and the like).

Onions and tomatoes present unique cases in that the same technique is used for both dicing and chopping. One could argue, though, that when dicing an onion or tomato (as opposed to chopping it), special care should be taken to make evenly spaced cuts so that the pieces are as uniform as possible.

A diced carrot (shown left) is cut into neat cubes, whereas a chopped carrot can consist of more irregularly shaped pieces.

Yield of a Diced or Chopped Onion

Not sure how many onions you need to buy or prep for a recipe? Here's our handy guide to approximate the yield in cups, depending on the size of your onion.

  • Small onion (about 2 inches in diameter) = 1/2 cup
  • Medium onion (about 2 1/2 to 3 inches in diameter) = 1 cup
  • Large onion (about 4 inches in diameter) = 2 cups