How To Dice An Onion – Fast

There are some techniques that, when you have been doing them for awhile, seem so natural and automatic it comes as something of a shock to learn some people don’t know about them.

For me, this is one such technique: How To Dice An Onion

It will almost certainly take you longer to scroll through these pictures than it will to dice an onion once you have this technique down. How far apart you slice will determine how large your onion pieces are. Narrow slices = small pieces. Wide slices = bigger chucks. Either way, the result is uniform pieces of onion in a minimum amount of time.

Note that you will be holding your onion together and down against the cutting board with your non-knife hand as you slice. If you don’t see my non-knife hand in these pictures it’s because it was holding the camera to take photos. This is, like most knife work, a two handed job.

Get your onion. Peel it, and trim the root end flush but don’t carve it out. The stem will help hold the onion layers together as you cut.

Cut your onion in half. We’ll dice one-half at a time. Note the stem, still holding together most of the onion layers.

We’re going to cut radial slices around the onion half without cutting through the stem. Picture the spokes of a bicycle tire. Now picture it’s just half a tire, with all the spokes radiating outward from the center. If you can imagine cutting along imaginary spokes as you slice your onion, this technique will be a cinch.

The first cut will be at a very shallow angle.

The next will be slightly less shallow as you slice your way towards the top of the onion.

Remember not to to cut through the stem – stop your slices 1/2-inch or so shy of the root end.

By the time you are slicing down through the center (apex) of the onion, your knife should be vertical.

Slice your way down the other side of the onion, making increasingly shallow cuts as you approach the cutting board on the other side.

When all of your radial slices are made, your onion will look something like this:

Now, turn your onion 90-degrees so that you can hold the root end firmly in your left (or non-knife) hand while slicing down and perpendicular to the radial slices you just made.

As you slice down, tidy little diced onion pieces will fall from your knife.

The onion will try to splay apart as you cut down. You have to use your non-knife hand to hold the onion together. My thumb and fingers spread out a bit down the sides of the onion to hold all the layers together.

Basic knife safety: keep the finger tips of your non-knife hand tucked firmly back and firmly against the food. The knife should be guided by the flat part of your fingers between the second and third knuckles of the non-knife hand. Yes, that’s right – the safest way to use a knife actually involves letting it rest against your other hand. See how my thumb is sticking out in this picture? It’s that way because it’s squeezing the onion layers together, but that positioning is not ideal. A moment of inattention and that thumb could creep forward and I could slice the tip of my thumb off. Ask me how I know this.

The final result as the diced onion falls from the knife.

After the majority of the onion is diced up, I chop up the usable onion around the core, too. It’s not a lot, and if you don’t want to add that extra step you could toss it in the freezer for stock day, but hey – waste not, want not, right?

This was the end result of three medium onions.

They yielded just over 3 cups of diced onion.

Don’t let the gratuitous number of photos fool you. This technique, once you’ve practiced it a bit, is probably the fastest manual way to dice an onion. I timed myself and it took me exactly 30 seconds to halve and dice one (already peeled) onion. Fifteen seconds per half. These three cups could be done in under 2 minutes without any rush at all.

And, as it happens, tomorrow I’m posting a recipe that calls for three cups of diced onion.

Hope this helps your allium wrangling.


  1. says

    Thanks for the tutorial…I'd been doing it backwards and had a hard time keeping things together. Any ideas on how to keep the tears away?

  2. Mama Turtle says

    I do it either way, depending on the shape of the onion, but I never leave the stem on like that. That style's good for wide flat onions but round ones seem to do better the "backwards" way for me. To each their own. To prevent tears I either set the cutting board on the stove and use the exhaust fan, or I point the standing fan at the counter on low. They won't make you teary if the onion air never makes it to your eyes.

  3. says

    Thank you, I used this method last night and it worked perfectly! I also passed it along to my coworkers, mostly self taught cooks at our tiny coffee house.

  4. says

    That looks so easy! I cook a lot, yet I always struggle with dicing onions – now I can't wait to give it a go – thanks for sharing!

  5. says

    Yay! I already knew this technique from my Mom actually. But it’s good to know there is person out there share this great technique to others. It does save the time.


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