How to Cut an Onion

You still might cry, but at least you’ll know you’re doing it right.

By Izzy Johnson
Aug 3, 2022
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There’s arguably nothing more basic in the kitchen than knowing how to cut an onion. Soups, stir frys, pasta dishes —if you can think of a dish, there’s likely an onion in it. Onions are an essential part of building flavor and are used in nearly every cuisine. Chances are, if you’re reading this, you have cut at least one onion before in your life.

But do you know how to cut an onion the right way? Cutting an onion can be challenging—and we’re not just talking about the tears. In order to make sure your final product is evenly sized, there are steps you need to follow. Prep cooks everywhere chop them up at a rapid pace on a nightly basis. And with a little instruction and practice, you can too. Follow along to learn how you too can cut onions as quickly and evenly as possible.

Get the Right Tools

The first step to cutting an onion is having the right knife for the job. While you use pretty much any large knife, we prefer our Santoku. The fluted blade keeps pieces of onion off the knife and where they belong—in little piles on your board. Plus, the 7-inch length of the blade gives you slightly more control than the larger Chef Knife. However, you can't go wrong with a Chef Knife.

How to Slice an Onion

Slicing is maybe the most basic cut and the process is very straightforward. Sliced onions can be cooked down and caramelized, used raw as a garnish, or quick pickled for a delicious addition to tacos. Most recipes call for a relatively thinly sliced or julienned onion, as to not detract from the texture of the dish.

Step 1: Trim the Ends

First, trim off both the root and stem ends of the onion, holding the onion still with your non-dominant hand. Be careful as it may rock a little. This will make the onion easier to peel.

Step 2: Slice in Half

Next, using the flat surface you’ve created to rest the onion on, slice it in half lengthwise. Remove the skin from each half of the onion—both the thin, papery skin and the second layer underneath as well.

Step 3: Make Perpendicular Cuts

Make a series of perpendicular cuts along the onion, cutting it pole to pole if you imagine it as a globe. This ruptures fewer cells, creating a smoother texture and more pleasant flavor. Keep the tip of your knife in constant contact with your cutting board and simply move the rest of the blade up and down. You can make these slices as wide or narrow as you like, depending on their desired use. Repeat with the other half of the onion to complete your slicing.

How to Dice an Onion

Dicing comes in three different sizes, each with their own application. Large diced onions (usually ¾ of an inch) can be used in a kebab or to flavor a stock. Medium dice (½ an inch) can be found in slightly more rustic soups or stew, while small dice (¼ inch) is used for a smoother sauce or eaten raw in salads or salsas. Here, we teach you how to make a medium dice, which you can scale up or down as needed.

Step 1: Trim the Ends

Begin by trimming off the stem. Hold the knife in your dominant hand and steady the onion with your other. Be careful as the onion is round and may rock a little. You want to trim off about ½ an inch of the onion above the stem.

Step 2: Slice in Half

Next, remove the skin and second layer just as you would in the slicing instructions above. Use the flat surface you’ve created to rest the onion on, and slice it in half lengthwise. Now you’re ready to cut.

Step 3: Slice Horizontally

Lay your onion halves flat and make a series of horizontal slices through its x-axis. You want to slice almost all the way though, stopping at the root. Be very careful of your fingers—keep them in a claw-formation to grip the onion and keep them out of the way.

Step 4: Slice Vertically

Make several vertical cuts along the onion’s y-axis, again keeping the root intact. Do your best to evenly space them alongside your horizontal cuts. Tuck your thumb behind the curved fingers of the hand holding the onion in so you don’t cut it. It is also helpful to use your knuckles as a guide, holding the side of your blade against them.

Step 4: Complete the Dice

Finally, complete the dice by making another series of vertical cuts perpendicular to the ones you just made. Again, you can use your knuckles as a guide. Continue to cut until you reach the root, rotating 90 degrees to make sure the onion stays stable in your hand and doesn’t start to fall apart. Repeat with the other half. Now you should have a perfect medium dice. If you want a smaller or larger dice, make your cuts farther apart or closer together. For a large dice they will be about ¾ of an inch apart and for a small dice, about ¼ inch.

Other Tips

Now that you know the two most basic cuts for onions, here are a few things to keep in mind. First, build your confidence with larger cuts first before moving on to smaller ones.

Next, when you’re transferring your onions from one place to another, don’t use the sharp end of your knife, it will dull the blade. Instead, use the flat side of your blade or a bench scraper, which is designed for this purpose.

Finally, if you are using the onion raw but want less of that oniony bite, don’t let your onions sit for too long, they get more pungent. You can also rinse them under running water to remove the bite as well.

How Can I Stop Crying?

It’s okay to cry. Cooking can be a good way to release pent up emotions (tenderizing meat, kneading dough) so if you actually need a good cry, cutting onions might be a good activity for you. That said, depending on the volume of onions you’re processing, the constant tears may get a bit annoying.

Using a sharp knife helps reduce tears because it keeps the onion’s cells more intact, thus releasing less of the chemical compound that makes us tear up. Cold water will also lessen the effects of this chemical, so you can chill your onions up to 30 minutes in advance or keep a wet paper towel next to your cutting board like some chefs do. If you have especially sensitive eyes, you can also opt for protective eyewear.

Ready to Learn More?

Dicing and slicing are two crucial cuts for any home cook to learn. Chef Sarah Heard from Austin’s Foreign and Domestic shows off a few more that are helpful for everyday use, including the julienne and the chiffonade. Follow along and continue to hone your skills one technique at a time.