Slicing onions is easier than you might think! In this tutorial, we will walk you through the simple step-by-step process of how to slice an onion crosswise with clear instructions and helpful tips.
Whether you're a total beginner in the kitchen, or want to improve your chopping skills, this guide is for you.

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What You'll Need
- Onion: Choose onions that are firm and free from soft spots, bruises, or mold. The outer skin should be intact and dry, without any signs of shriveling. You can use this technique for all types of onions, from red onions to yellow onions or sweet onions.
- Chef's Knife: A chef's knife has a wide and sturdy blade that can easily slice onions. Make sure to use a reliable, sharp knife. If your knife is dull, you will have a much harder time cutting the onions.
- Cutting Board: The best type of cutting board for slicing onions is one made of wood or plastic. Both wood and plastic boards provide a stable surface for cutting. Make sure your cutting board is not warped and is placed on a flat, even surface.
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How to Slice an Onion, Step-by-Step
Step 1: Set Up Your Space
Place a clean, sturdy cutting board on a flat surface. Make sure your knife is sharp, clean, and ready to use.

Step 2: Trim and Halve the Onion
Place your onion on the cutting board. Carefully trim off the stem end, but leave the root end intact. This helps hold the onion together while you slice.

Slice the onion in half from the root end of the onion to the stem end. Your knife must be sharp to prevent crushing or tearing the onion layers.

Step 3: Peel the Onion
Peel off the papery skin of the onion from both halves and throw it away.
Place the two onion halves flat-side down on the cutting board. This creates a stable surface for slicing, preventing the onion from rolling around.

Step 4: Start Slicing
With both cut sides of the onion facing flat-side down, begin making vertical cuts crosswise. Aim for uniform slices of your desired thickness, whether paper-thin for salads or thicker for sauteing.
Proper Slicing Technique
Ensure you're using the proper slicing technique to achieve consistent results: keep your fingertips tucked safely away from the blade, and use a smooth, steady motion to slice through the onion. Remember - you absolutely need a sharp chef's knife for this.
(As an extra tip, remember not to wipe your eyes with your onion-hands. This is never fun.)

Adjust Thickness as Needed
Feel free to adjust the thickness of your sliced onions depending on the recipe you're making or your personal preference. Thinner slices cook faster and blend more seamlessly into dishes, while thicker slices add texture and visual appeal.
For example, thin slices are perfect for topping salads or offering great flavor to wrap sandwiches or burgers, while thicker slices make great caramelized onions, onion rings, or cooked alongside peppers with sausage.
Step 5: Repeat with the Other Half
Once you've finished slicing the first half of the onion, move on to the second half and slice it the same way. Make sure to be consistent with the size of the slices.
Optional Step: Dicing the Onion
If you need diced onion, not slices, see our guide on How to Dice an Onion. We have plenty of tips for you here! Chopped onions are great for cooking into soups, stews, salsas, sauces, dips, and more.

Storing Sliced Onions
Once you've cut onions, you want to store or use them immediately. Store sliced onions in an airtight container or resealable plastic bag in the refrigerator. As long as you store them properly, sliced onions can last for up to one week in the fridge.
Give these guides a try, too!
Ways to Use Sliced Onions
- For Fajitas: Try making our Air Fryer Peppers and Onions using this guide for slicing onions and use it as a base for veggie fajitas with toasty tortillas, cheese, guacamole, and sour cream. You can mix in a protein, too! How about some sliced thin chicken breast?
- On Sandwiches: Use sliced onions as a topping for our Air Fryer Chicken Sandwich, or go a little wild with your next BLT sandwich by adding onions.
- In Potato Hash: We love a good hash for breakfast - what about you? Try our Air Fryer Potatoes and Onions!

Safety Tips
Always cut away from yourself. Keep your knuckles parallel to the knife and be sure to never extend your fingers when slicing. Make sure your hands, the onion, and the surface the onion is on are all completely dry and stable. And remember: your knife must be sharp for cutting onions!
If you're a novice, a little bit clumsy, or just want to be extra safe, cutting gloves can make all the difference!
Tips for Preventing Tears when Slicing Onions
Everyone's least favorite part of slicing onions is the infamous onion tears. Thankfully, you can reduce the sting following a few simple tips:
- Use a Sharp Knife: The best option is to use a sharp knife. A sharp knife creates cleaner cuts, which can minimize the release of the compounds that cause tears. Dull knives can crush the onion cells, releasing more irritants.
- Chill the Onion: Place the onion in the refrigerator for about 30 minutes before slicing. Chilling the onion can help reduce the release of the compounds that cause tears.
- Wear Goggles or Glasses: Protective eyewear, such as goggles or glasses, can create a barrier between your eyes and the onion vapors, preventing tears. You might feel silly for wearing goggles in the kitchen, but you won't feel silly when your eyes aren't burning.
- Freeze the Onion: Some chefs suggest freezing the onion for about 10-15 minutes before slicing. Freezing can help reduce the release of tear-inducing compounds.
Why do onions make you cry? Onions absorb the minerals in the soil they're planted in, and those minerals happen to include sulfur that forms the onion's amino acids. When you slice an onion, you're slicing through its cells. This results in a combination of chemicals, creating fumes that vaporize. Your eyes naturally water as a reaction to protect themselves. See our source if you're as fascinated by that as we are!
Any questions?
If you have any questions, feel free to contact us, or reach out in the comments below the printable recipe card. We love to hear from you and are always happy to help.

How to Slice an Onion (with Video)
Equipment
- Chef's knife
- Cutting board
Ingredients
- 1 onion medium to large
Instructions
- Place a clean, sturdy cutting board on a flat surface. Make sure your knife is sharp, clean, and ready to use.
- Place your onion on the cutting board. Carefully trim off the stem end, but leave the root end intact. This helps hold the onion together while you slice.1 onion
- Slice the onion in half from the root end of the onion to the stem end. Your knife must be sharp to prevent crushing or tearing the onion layers.
- Peel off the papery skin of the onion from both halves and throw it away.
- Place the two onion halves flat-side down on the cutting board. This creates a stable surface for slicing, preventing the onion from rolling around.
- With both cut sides of the onion facing flat-side down, begin making vertical cuts crosswise. Aim for uniform slices of your desired thickness, whether paper-thin for salads or thicker for sauteing.
- Once you've finished slicing the first half of the onion, move on to the second half and slice it the same way. Make sure to be consistent with the size of the slices.
Notes
- Keep your fingertips tucked safely away from the blade, and use a smooth, steady motion to slice through the onion.
- Remember not to wipe your eyes with your onion-hands.
- Feel free to adjust the thickness of your sliced onions depending on the recipe you're making or your personal preference. Thinner slices cook faster and blend more seamlessly into dishes, while thicker slices add texture and visual appeal.
- Thin slices are perfect for topping salads or offering great flavor to wrap sandwiches or burgers, while thicker slices make great caramelized onions, onion rings, or cooked alongside peppers with sausage.
- If you need diced onion, not slices, see our guide on How to Dice an Onion.
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