How To Dice An Onion

Peeling and Chopping an Onion Is Easier Than You Think With This Step by Step Guide

By
Omid Roustaei
Headshot of Omid Roustaei in kitchen wearing a striped apron
Omid Roustaei
Omid Roustaei is an Iranian-American psychotherapist, recipe developer and culinary instructor, who is passionate about healthy and improvisational cooking, often incorporating Persian influences.
Learn about The Spruce Eats' Editorial Process
Updated on 12/17/22
Tested by
Julia Hartbeck
Tested by Julia Hartbeck
Julia is a professional food photographer and stylist based in England. She loves nothing more than reading cookbooks cover-to-cover and traveling the world to sample international cuisines.
Learn about The Spruce Eats' Editorial Process
Prep: 10 mins
Cook: 0 mins
Total: 10 mins
Servings: 2 to 6 Servings
Yield: 2 Cups Diced Onion

Knowing how to peel and dice an onion is arguably the most important skill for any cook to know. The onion is often the most common first ingredient in just about every dish in just about every cuisine.  Perhaps for the same reason, the best technique for dicing an onion is a matter of continuous debate, and it is important to acknowledge that there is no single right way. The instructions below use insights from professional chefs but have also been simplified to be comfortable for home cooks.

A cutting board with a peeled onion being diced with a knife

The Spruce Eats / Julia Hartbeck

How To Cut An Onion Without Crying

The key to preventing tears really comes down to one simple factor: exposure, both in time and to the surface area of the cut onion. So it is best to keep any cut parts of the onion facing down while you continue to slice and dice efficiently, quickly and safely. But personally, when an onion moves me to tears, I see it as a sign to reflect on unprocessed emotions, and welcome it as an opportunity to cleanse my tear ducts!

  • Creating airflow by working near a vent hood or an open window if possible
  • Chilling the onion by placing it in the freezer for 15 minutes, or in the refrigerator for longer
  • Draping a damp paper towel over the cut parts of the onion as you work on the other parts

There are also some fun urban legends around ways to prevent tears when cutting onions:

  • Placing an unlit match in your mouth, secured by your front teeth
  • Placing a damp paper towel near the cutting board
  • Placing a piece of bread in your mouth
  • Wearing contact lenses or swimming goggles
  • Lighting a candle near your cutting board

How Many Cups Is One Diced Onion?

The quantity yielded from a single diced onion varies based on the size of the onion.

  • 1 medium onion yields about 2 cups of diced onion
  • 1 large onion yields about 3 cups of diced onion


The Best Knife For Dicing An Onion

It may go without saying that this process begins and ends with the right knife.

  • Most important is sharpness: a dull knife will have you exerting more force than necessary, which can lead to the onion slipping on the cutting board and potentially causing an accident. You can sharpen your knife using a whetstone, and then maintain the sharpness using a steel each time before you use the knife.
  • The best knife for cutting an onion is a chef's knife. Paring knives are not ideal because their short blade length means that you are pressing down rather than slicing across, so you are more likely to squash the onion out of shape, yielding an uneven dice.

"This is a tried-and-true method of dicing an onion that even the kitchen professionals use. Don’t be scared by the number of steps - it will quickly become your favorite way to dice quickly and efficiently. Just remember to start with a sharp knife and tuck those fingers in!" —Julia Hartbeck

How To Dice An Onion/Tester Image
A Note From Our Recipe Tester

Ingredients

  • 1 whole medium onion

Steps to Make It

  1. Gather the ingredients and a sharpened chef's knife.

    whole white onion on cutting board with chef's knife

    The Spruce Eats / Julia Hartbeck

  2. Place the onion on its side on a cutting board, with the root and stem ends facing outward (9 o'clock and 3 o'clock on a clock face).  Holding the onion firmly, slice off the top 1/4 inch of the stem end and discard. Leave the root end in tact.

    stem end of whole onion being cut off with a chef's knife

    The Spruce Eats / Julia Hartbeck

  3. Place the onion on the cutting board with the cut surface facing down, and the root end sticking up, and slice vertically all the way through, creating two equal halves.

    whole onion being cut with chef's knife in half through root end

    The Spruce Eats / Julia Hartbeck

  4. Peel the skin and the outer layer off of each half of the onion and discard them. Remove any additional bruised, discolored, or unhealthy layers as needed.

    two halves of peeled onion on a cutting board with peel set off to side

    The Spruce Eats / Julia Hartbeck

  5. Place one half of the onion flat side down on the cutting board with the root end facing away from you (12 o'clock on a clock face).

    one half onion cut side down on cutting board with chef's knife

    The Spruce Eats / Julia Hartbeck

  6. Make parallel vertical cuts with the knife tip starting almost at the root end, but not cutting through the root end. The cuts should be about 1/4 inch apart. The root end should still be intact, keeping the half onion together.

    half of onion being cut using chef's knife, parallel vertical cuts toward root end

    The Spruce Eats / Julia Hartbeck

  7. With the cut surface still facing down, rotate the onion so that the root end is facing outward (9 o'clock).

    half onion with parallel vertical cuts resting on cutting board, with root end at 9 o'clock

    The Spruce Eats / Julia Hartbeck

  8. Make parallel horizontal cuts almost all the way across the half onion, until you just reach the root end. These cuts should also be about 1/4 inch apart. This is the most critical time to hold your knife securely and keep your fingertips tucked in.

    half of onion being sliced horizontally with chef's knife on a cutting board

    The Spruce Eats / Julia Hartbeck

  9. Holding the half onion securely, with your fingertips tucked in, slice the onion vertically, about 1/4 inch apart. This will yield an even, 1/4 inch dice up to the root end. This root end can be discarded or frozen in a bag with other vegetable scraps to make veggie stock.

    half of onion being cut again vertically, on a cutting board with chef's knife, to result in diced onion

    The Spruce Eats / Julia Hartbeck

  10. Repeat steps 2 through 9 with the other half of the onion.

    diced onion on a cutting board with chef's knife and root ends set aside

    The Spruce Eats / Julia Hartbeck

Tips To Easily Dice An Onion

  • Before starting the process remove any loose, papery outer skin, which can cause the knife to slip.
  • Keeping the root end intact until the very end helps to keep the onion stable and safe to work with.
  • When slicing, always hold your knife securely, and keep the fingertips of your other hand tucked in and pressed firmly into the onion. This will not only secure the onion on the cutting board, but also protect your fingers.


How To Store Diced Onions

Diced, chopped, or sliced onions can be stored in an airtight container or zip-top bag in the refrigerator for up to five days.

Nutrition Facts (per serving)
7 Calories
0g Fat
2g Carbs
0g Protein
×
Nutrition Facts
Servings: 2 to 6
Amount per serving
Calories 7
% Daily Value*
Total Fat 0g 0%
Saturated Fat 0g 0%
Cholesterol 0mg 0%
Sodium 0mg 0%
Total Carbohydrate 2g 1%
Dietary Fiber 0g 1%
Total Sugars 1g
Protein 0g
Vitamin C 1mg 4%
Calcium 3mg 0%
Iron 0mg 0%
Potassium 26mg 1%
*The % Daily Value (DV) tells you how much a nutrient in a food serving contributes to a daily diet. 2,000 calories a day is used for general nutrition advice.
(Nutrition information is calculated using an ingredient database and should be considered an estimate.)

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