When you know how to cut an onion the right way, your mealtime prep will be a whole lot easier! This tutorial will show you how to slice and dice onions for all your cooking needs.

Overhead view of sliced onions cooking in skillet
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Before you master how to make a perfect quiche or homemade pasta from scratch, it’s important to know the fundamentals of cooking. And there’s nothing more fundamental than knife skills.

How to Cut an Onion

Knowing how to use a knife properly is an essential part of being a great cook. One of the best ways to hone your knife skills is to learn how to cut an onion using proper technique.

It may seem simple, but it can be surprisingly tricky if you don’t know what you’re doing.

(Need some ideas for using your onions? Try my Homemade French Onion Dip or Onion Tart!)

Prepping an Onion

First thing’s first: you’ll need to remove the skin and ends from the onion before you get started.

An onion has a stem end and a root end. The root end is the end with the dry brown roots coming out, while the stem end is the end that faces up when the onion is in the ground—it’s where the green sprouts grow.

Place the onion on a cutting board on its side, then cut 1/2-inch from the stem end and a smaller slice—about 1/8-inch—from the root end.

Turn the onion so the stem end is on the bottom and the root end is facing up towards you. Cut the onion in half from root to stem.

With the onion halved, it’s now easy to peel off the skin and discard it. You’ll want to discard not only the papery skin on the outside, but also any layers underneath that feel leathery and thin—these layers can be tough and difficult to chew.

Skillet on stovetop with sliced onions and wooden spoon

How to Slice an Onion

  1. Step 1 – Place one of the halves flat side-down on your cutting board and start slicing crosswise to form half moons. 
  2. Step 2 – Continue slicing until you reach the end of the onion.
  3. Step 3 – Repeat with the other half.

How to Dice an Onion

  1. Step 1 – Place one of the halves flat side-down on your board and make angled lengthwise cuts from the stem end towards the root end—but don’t cut through the root end.
  2. Step 2 – Hold the root end and slice the onion crosswise starting with the stem end and working your way to the root end. Discard the root end.
  3. Step 3 – Repeat with the other half.
Sliced onions in a pan, for a guide on how to cut an onion.

Tips

  • Leaving the root end partially intact will hold the onion together as you cut, making the process a lot easier!
  • The sharper the knife, the better! It makes it so much smoother to cut.
wood cutting board

Tools to Use

  • Chef’s knife – The sharper the better!
  • Cutting board – I recommend using a non-slip board when you’re cutting onions.
Stack of homemade onion rings on a piece of butcher paper.

Other Methods

Rings

If you’re making onion rings, you’ll need to remove the root and stem ends, then peel the onion. 

To keep the onion from rolling on the cutting board, slice a thin sliver from one side. Place that side down on the board, then cut the onion into rounds in your desired thickness.

Wedges

If you want to cut your onion into wedges, follow the steps for dicing, but stop after making the angled lengthwise cuts.

Storage Tips

If you’re not going to use all of a cut onion right away, store it in an airtight container or wrap it tightly in plastic wrap and keep it in the refrigerator. Cut onions will last up to a week when stored properly. 

Frequently Asked Questions

Do you cut the root or stem of an onion?

Leaving part of the root end on the onion will help it hold together when you slice it. One of the most common mistakes people make with cutting onions is chopping off both the stem and the entire root end, which makes the onions slip when you cut them.

How do you prevent tears when slicing onions?

Try slicing the onion near an open window so the fumes don’t irritate your eyes, or turn on the fan in your kitchen and cut the onion nearby. If you have time, you can also freeze the onion for a few minutes. 

What is the best knife for cutting an onion?

The best knife for cutting an onion is a sharp chef’s knife. It will make slicing through the layers of the onion much easier and faster; in addition, a sharp knife can make you less likely to cry when you’re cutting.

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