How to Cut an Onion

Learn how to cut an onion with this tear-free, step-by-step guide. This tutorial shows you how to safely peel, slice, dice, chop, and mince onions. It has everything you need to know!

The first knife skill I learned in culinary school was how to cut an onion properly. It’s the one technique I use with almost every savory recipe. The earthy, sulfurous allium adds a pungent taste when raw or infuses sweet notes when cooked.

There are various types of onions (Allium cepa), from more intense and savory to sweet. Knowing how to hold and cut an onion into different shapes safely is essential for any home cook to master. Since they are round, they are tricky and dangerous to maneuver on a flat surface, but I’ll show you how.

Safety tips

• Use a sharp and honed knife: A dull knife makes it difficult and more dangerous to slice. Sharpen when the blade is blunt. Use honing steel before you get started to bring the knife’s edges back to the center for more crisp, clean cuts.
• Where to cut on the blade: The sharpest part of a chef’s knife is towards the center, about 3 to 4 inches from the tip. Start the horizontal and vertical cuts from the center of the blade, then down to the pointed end to make cutting easier.
• Protect your fingers: Use the free hand to hold the onion using a claw-like grip to prevent cutting your fingertips. This technique involves tucking your fingertips in so that the knuckles parallel the blade but not so close that it’s touching. Move your clawed hand slightly further back the distance of the next cut as the blade starts to go up for the next slice.

Trim the ends

• Use a sharp chef’s knife to trim the stem end by about ½-inch.
• If slicing, trim just past the root end, about ¼-inch to make it easier to slice through.
• If dicing, trim the root end to remove any long strands but keep the bulb intact, so the layers don’t come apart. Also, do this for slicing wedges.

Cut in half

Place the onion on the cutting board stem-side down. This spot gives the round onion a stable flat surface to sit on. Cut lengthwise from the root down to the stem. This action is called “pole to pole.” Now you have two halves.

Chef’s Tip: Keep the cut sides down on the board to reduce sulfur compounds from making you tear up.

Peel the skin

Use your fingers to peel away the papery skin starting from the stem end. If needed, remove the first layer of the onion to make peeling easier.

How to slice an onion (2 ways)

Option 1) Cut Lengthwise: Slice “pole to pole” or lengthwise, following the grain. Use the long stripes on the onion as a guide. This option yields sturdier pieces when cooked. Slicing with the grain gives a milder flavor because it ruptures fewer cell walls and releases fewer sulfur molecules.

I prefer this method when sauteing, stir-frying, or long cook times in soups and stews.

Option 2) Cut Crosswise: Slice through the equator horizontally, going against the grain. This option yields perfectly arched pieces with more intense flavor because more sulfur compounds are created. Cutting against the grain also softens the texture as the fibers will not hold as tightly together.

I prefer this method when adding to salads, burgers, or pickling. It’s easier to chew and break down when enjoyed raw, in soups, sauces, or if you want softer bites in cooked dishes.

How to slice an onion into wedges

Keep the root end intact so that the onion layers stay together. After halving lengthwise and peeling, place one of the halves cut-side down on the cutting board. Make radial cuts towards the center to give a wedge shape.

I use this method when making roasted chicken or turkey, or making a braise. The wedges ultimately soften, absorb flavor, and make for a delicious side dish when cooked.

How to cut an onion into rings

Trim off the root end by ¼-inch and the stem end by ½-inch to make peeling the skin easier. Cut an additional ¼-inch slice from the middle. Place the onion on the board, middle cut-side down for stability and prevent it from rolling away. Firmly hold the onion and make cuts crosswise through the equator to achieve rings of your desired thickness. Add to stovetop burgers, sandwiches, pickling, and fried onion rings. 

You can also use a mandoline to make rings. Be careful when holding the onion, as you don’t want to cut your fingertips on the blade.

How to dice onions (3 ways)

Option 1) Traditional Method: Make horizontal cuts parallel to the cutting board. Hold the onion down with your fingertips or press down with your palm and point your fingers up. Make about 1 to 3 cuts, depending on how small a dice you want. Do not cut through the root end as it holds the onion together.

Now make vertical cuts lengthwise, starting about 1-inch from the root end. The width determines how large the dice will be. Rotate the onion so that the root end is in the back. Make slices down perpendicular to the other cuts. Let the claw-holding technique guide the knife cut so you don’t knick your fingertips.

Option 2) Angled Method: Try this technique for those not comfortable making horizontal cuts. Start by making cuts lengthwise at about 60-degree radial down towards the board, not through the center of the onion.

This angle will give more precise cuts instead of lots of smaller pieces towards the center. Now make perpendicular cuts down to provide the desired dice size. Not the most uniform method, but it’s quick.

Option 3) Vertical Method: Another way to eliminate horizontal cuts is a technique involving making a series of vertical cuts on two different sides of the onion. Once the onion is halved, cut that down the center lengthwise to make four pieces. Work one by one, making vertical cuts, 1-inch from the root end on each quartered piece. Flip those over onto the sides you just cut so that the cuts are horizontal. 

Proceed with making vertical cuts, 1-inch from the root end on the sides now facing up. You can push two quarters together to look like an onion half or keep them separate. Hold them together with the claw, and slice horizontally down to create diced pieces. It gets easier to do once you’ve tried this a few times.

Dicing vs. chopping

Dicing involves more precise, uniform cuts, resembling a flat square shape. This cut is essential when you want a more definitive onion appearance in dishes like stir-fries, soups, stews, homemade salsa, or dips.

Chopping has an irregular shape that can be large or very fine. The appearance is not essential, as you may not see it in the dish. Chopped onions tend to produce more flavor due to more enzymes released. I use this method when making pureed soups, stuffings, meatloaf, meatballs, or aromatics for a sauce.

Diced onion terms

• Minced: Tiny pieces, ⅛-inch or smaller
• Chopped Fine: Small pieces, ⅛ to ¼-inch
• Chopped Medium: Pieces ¼ to ½-inch
• Chopped Coarse: Larger ½ to ¾-inch pieces

Why do onions make your cry?

Uncut bulbs sitting in your pantry or counter have a minimal aroma. But just like when you mince garlic, when cut, suddenly a strong, pungent odor appears. When the cell walls are cut, the enzyme alliinase releases and reacts with the isoalliin compound. Also, another flavor compound forms, propanethial-S-oxide (PSO), giving the raw, stinky sulfurous taste.

The volatility of PSO causes tears in your eyes, intensifying the more you chop. It stings because the compounds convert to sulfuric acid when it mixes with the water in your eyes. The more cuts you make and the longer it sits before cooking, the more sulfur atoms release, making the smell, taste, and tears more intense.

How to cut an onion without crying

• Use a sharp knife: It helps make clean, thin slices, reducing unwanted cell wall damage, which causes your eyes to tear up from the volatile sulfur compounds.
• Wear eye protection: Contact lenses cover the eyes from those unwanted sulfurous lacrimators. I can attest to that! If you have goggles from science class, wear those.
• Turn on a vent: Cut the onions near a vent so that the volatile compounds get sucked away. You can also open up a nearby window to help with the airflow. 
• Leave the root end intact: Besides keeping the onion together when dicing or slicing into wedges, it can reduce the number of tears. The root end has a higher amount of sulphuric compounds.
• Cover the cuts: After slicing, immediately place the exposed sides down on the board in between cuts. If cutting many onions, place the slices or cuts in a container, and cover with a lid.
• Chill it: Chilling slows alliinase enzyme activity and reduces the rate at which the volatile sulfur compounds produce. Refrigerate the onions for at least 30 minutes, up to 2 hours. Any longer and the starches will turn to sugar, turning soft, and change the flavor. Freeze for 15 to 45 minutes max, you don’t want it frozen, or it will change the texture and be hard to slice.

Selecting

Pungent onions contain less water, so they will feel smooth, firm, heavy, and have thicker skins, with drier tighter necks. Mild and sweeter onions have more give, thinner skins, and broader necks. Avoid onions with bruises or mushy spots, as they will rot quickly.

Storing

Cut onion pieces will intensify in flavor and aroma. If stored properly in the refrigerator, use them within 7 to 10 days—store in an airtight container, like glass, to reduce odor. You can also place them in a resealable plastic bag, then inside a plastic container for a double barrier. 

I find that storing half an onion wrapped in foil or plastic wrap, then in a bag or container, keeps the onion from drying out and stinking up the fridge. They freeze well in a resealable plastic bag for up to 6 months. It’s best to use frozen onions in soups, stew, or sauteed in a dish. No defrosting is needed.

Ways to use onions

• Caramelized onions for a topping
• French onion soup
• French onion dip
• To flavor meat mixtures like meatballs
• An aromatic for soups, stews, and sauces

Frequently asked questions