Onions around a board of diced onion

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Always wanted to know how to chop like a pro? Sharpen up your knife skills and learn how to dice an onion like a chef, with super-fine results, minimal food wastage and all your digits intact!

If this is your first time trying to dice an onion properly then give yourself time to practice each step. Once you have mastered the technique it will get quicker over time!

What equipment do I need?

You don’t need any fancy equipment to dice an onion professionally. You simply need:

  • Chopping board – make sure it’s held securely in place and doesn’t slide around on the worktop. Pro tip: use a slice of damp paper towel underneath to help hold it in place.
  • Knife – Use a large chef’s knife if you have one, but you can also use a smaller knife. Just make sure that it’s longer than the onion itself. Most importantly: make sure the knife is super sharp. It’s actually more dangerous to slice with a blunt knife as it is more likely to slip, and you’ll need to use more pressure for each cut. A blunt knife is also more likely to make you cry when chopping an onion – more about that below!

How to dice an onion

Time needed: 5 minutes.

Follow these step-by-step instructions to get great results every time you need to dice an onion.

  1. Cut the onion in half

    Cut the onion in half lengthways, this means cutting through the root and top of the onion, rather than cutting it through the middle.

  2. Identify the root of the onion

    The root of the onion is the end of the onion that has little stringy pieces coming out of it (ie, the roots). This is very important as this is the part of the onion you need to leave intact. Cut off the opposite end.

    Remove the skin from the onion.

  3. Cut slits down the length

    Place one half of the onion cut/flat side down on the chopping board and cut slits along the length of it, with each cut stopping a few millimetres from the root. The narrower the cuts, the finer the dice you will get.

  4. Slice parallel cuts through the middle of the onion

    Make two slices into the onion, from the side where you cut off the top end. One slightly above the centre and one slightly below. Again, leave a few millimetres from the cut and the root of the onion.

  5. Cut down the width of the onion

    Grip the onion with your middle finger on top and your thumb and little finger holding it together at the sides. Start to cut along the width of the onion, which will give the finely diced pieces. Again, the narrower the cuts, the finer the dice will be.

  6. Trim any excess from the root

    Finally, make some diagonal slices around the root of the onion, to get every last bit of onion flesh you can!

How to Dice an Onion step by step

What’s the difference between chopping and dicing?

Dice, chop, slice, mince. All terms you’ll hear when reading a variety of recipes. If you are wondering what the difference is between all these different things then read on:

  • Generally, a recipe calls for an ingredient to the chopped then this is similar to a dice, but with larger pieces.
  • On the other end of the spectrum, you may see instructions to mince something. This is even finer than a dice. You can achieve this by dicing the ingredients and then rocking your knife through the chopped ingredients until the pieces are really small.
  • If you see an ingredient referred to as sliced, then you simply slice along the vegetable.
Diced onion on a chopping board

How to stop crying when cutting an onion

The bad news is I have never found a method that completely stops the tears when slicing onions. And back in my days as a prep chef, I would chop a good 10kg (22lb) of onions a day. However, I also seem to have very sensitive eyes and even chopping leeks sets me off. So perhaps you will find a method that works more effectively for you.

It’s useful to understand why onions make us cry, before looking at some of the tips and theories that will help reduce the tears. Onions have their own in-built defence mechanism, to stop you from wanting to cut or bite into them. When sliced, the onion releases a chemical called syn-propanethial S-oxide. This vaporises when you cut into the onion and forms a gas. When this gets into your eyes your body triggers a tear response to wash away the irritating chemical.

While it may be difficult to completely stop the tears, there are a few things you can do to reduce the amount of irritation.


  • Wear googles – this does work to some extent, and logically it sounds like it should. Personally, as I have sensitive eyes, I would need to wear the googles for a good while after chopping the onion to stop any residue chemicals floating around in the air.
  • Use a super sharp knife – When you use a blunt knife you aren’t making clean slices through the onion, you are also squishing the cells in the onion which will squeeze and release more of the gas.
  • Freeze the onion – while I’ve not tried this it apparently works well. Personally, I can’t imagine that slicing frozen onion will be easy, and I think you’ll probably be replacing one problem with a different one. I also imagine it’s more dangerous to slice when slightly frozen since it will be tougher to cut into.

Some things that definitely don’t work involve holding water or a piece of bread in your mouth while chopping, breathing through your mouth, or chewing gum.

Now you know how to chop an onion perfectly, why not try out your new knife skills with one of these recipes?

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