How to Cut an Onion: Dice, Slice, Strips, Rings and Wedges (Without Crying)
Here's how to cut an onion the safe, even way: trim off the stem end, halve the onion through the root, peel each half and lay it flat side down. Keep the root on, because it holds the layers together. For dice, make lengthwise cuts towards the root and then cut across; for slices, cut from pole to pole; for rings, slice across a whole peeled onion. A sharp knife and a cold onion do most of the work against tears.
Onions are the first thing most of us cut every day, and the first job where a dull knife, a wobbly onion or a bad grip shows. Below you'll find the basic prep, then the cuts people actually search for: dice, slices, strips for fajitas, rings for burgers and wedges for kebabs. After that: how to cut an onion without crying, which knife suits onions best, and how to store what's left over.
Before you start: knife, board and grip
A medium onion is about the size of your fist, so you want a blade long enough to pass through it in one stroke. A chef's knife around 200 mm is the classic choice; a santoku of 175–180 mm does the same job with a flatter edge and a little less length. Both the Samura Mo-V chef's knife 200 mm (blade 46 mm high) and the Mo-V santoku 180 mm (blade 48 mm high) are tall enough that your knuckles clear the board while the edge is on it.
- Board. Wood or plastic, never glass. SAMURA's own care advice is to cut only on wooden or plastic boards. The Samura TPU board (380 × 250 mm, 2 mm thick) is an elastic surface the blade sinks into slightly instead of hitting.
- Grip. Pinch the blade just in front of the handle, curl the fingertips of your other hand under (the claw) and let the flat of the blade ride against your knuckles. Our guide to how to hold a knife walks through it.
- Sharpness. A sharp edge slides through the layers; a dull one crushes them, which releases more of the compounds that make your eyes sting, and it is more likely to slip. If your knife is squashing instead of slicing, read why knives lose sharpness and our guide to how to sharpen kitchen knives first.
How to cut an onion: the basic prep
- Trim the stem end. Cut off the pointed top, about a centimetre in. Leave the hairy root end alone for now.
- Halve through the root. Stand the onion on the cut end and slice straight down through the root, so each half keeps a piece of it. The root is what stops the layers sliding apart while you cut.
- Peel. Lift the papery skin with your thumbnail or the tip of a paring knife, taking the first slippery layer with it if it's bruised or dry.
- Lay flat. Put each half cut side down. A flat base means the onion can't roll under the blade, which is where most onion mishaps happen.
How to dice an onion
Dice is the cut for soups, sauces and most everyday cooking. There are two schools: the classic horizontal-cuts method and the simpler radial method. Both work; the radial one is safer for beginners.
Classic method
- With the half flat side down and the root pointing away from your knife hand, make two or three horizontal cuts parallel to the board, stopping short of the root. Keep your guiding hand flat on top of the onion, fingers well back.
- Make vertical lengthwise cuts from the stem end towards the root, again stopping just short of it. Closer cuts give a finer dice: 2–3 mm apart for a fine dice, about a centimetre for a rough chop.
- Turn the half 90 degrees and cut across in even strokes. The cubes fall apart on their own. Discard the root piece at the end.
Radial method (no horizontal cuts)
Skip the horizontal cuts. Instead, angle your lengthwise cuts towards the centre of the onion, like the spokes of a wheel, so each cut follows the curve of the layers. Then cut across as before. Because an onion is made of concentric rings, the angled cuts give you fairly even pieces without ever pointing the blade at your palm.
How to cut an onion in slices, strips, rings and wedges
Slices and half-moons
Lay the peeled half flat and slice across the grain (from side to side) for half-moons, the shape you want for salads, sandwiches and quick frying. The pieces are evenly thin and soften fast in the pan.
Strips for fajitas, stir-fries and caramelising
Slice with the grain instead: from the stem end towards the root, pole to pole, and trim the root last. These strips hold their shape when cooked, which is why they're the standard cut for fajitas, stir-fries and slow caramelised onions. Aim for 5 mm strips for fajitas, 2–3 mm if you want them to melt.
Rings for burgers and onion rings
Don't halve the onion. Trim both ends, peel it, lay it on its side and slice straight across. Thin rings (2–3 mm) go raw on burgers and salads; thicker rings (about 1 cm) are for battering and frying. A whole onion wants to roll, so hold it firmly with the claw and cut each slice in one stroke rather than sawing; push the rings apart with your fingers.
Wedges for kebabs, roasting and grilling
Halve the onion through the root and peel it, but this time leave the root intact. Cut each half lengthwise into three or four wedges, each with a sliver of root to hold the layers together. For kebabs, separate the wedge into two- or three-layer pieces so they thread onto a skewer without falling apart. For roasting, keep the wedges whole.
How to cut an onion without crying
When you cut into an onion, you break open its cells and release sulphur compounds that irritate your eyes. You can't switch that off, but you can cut down on how much reaches you:
- Use a sharp knife. A keen edge slices cells cleanly; a dull one crushes them and sets off far more of the irritant. This is the single biggest difference.
- Chill the onion. Half an hour in the fridge (or 10–15 minutes in the freezer) slows the reaction.
- Cut the root last. The root end carries the highest concentration of the compounds, so keeping it on while you dice helps twice: it holds the onion together and stays out of the air until the end.
- Work quickly, in moving air. An open window, an extractor fan or a small fan across the board carries the vapour away. Stand upright rather than leaning over the board, because the vapour rises straight up.
Which knife is best for cutting onions?
Any sharp kitchen knife with a blade longer than the onion will do, but the shape changes how the job feels. All the knives below have a double-bevel edge ground on both sides, so they cut straight without steering.
| Knife | Why it suits onions | Where it falls short |
|---|---|---|
| Chef's knife, 200 mm (e.g. Mo-V, 46 mm blade height) | Long enough for whole onions and rings; curved edge for rocking through a pile of dice; dicing onions is listed among its best uses | Heavier and longer than beginners sometimes like |
| Santoku, 175–180 mm (e.g. Mo-V, 48 mm blade height) | Tall, flat blade for straight up-and-down cuts; compact and quick for slices and strips | Less length for a very large onion; rocks less |
| Nakiri, about 167 mm (e.g. Mo-V nakiri) | Rectangular blade touches the board along its whole length, so every slice is cut through; dicing onions and cutting strips are in its product description | No tip for detail work; vegetables only |
If you cook a lot of vegetables, a nakiri is a joy on onions; our article on the nakiri knife explains why that flat edge matters. For everything else in the kitchen, the chef's knife or santoku is the better single purchase.
How to store an onion once cut
A cut onion dries out, takes on fridge smells and gives its own smell to everything around it. Wrap the cut half tightly in cling film or put it cut side down in a sealed container, refrigerate it and use it within a few days. Diced or sliced onion keeps the same way, and it freezes well for cooking: spread the pieces on a tray, freeze, then bag them. Don't store cut onion at room temperature. And wash and dry the knife straight away: onion juice is acidic, and even a corrosion-resistant stainless blade is better off without it.
FAQ: cutting onions
How do you cut an onion without crying?
Use a sharp knife, chill the onion first, keep the root end on until the last cut and work in moving air. The sharp knife matters most: a clean cut releases far less of the eye-stinging vapour than a crushed one.
How do you properly cut an onion?
Trim the stem, halve through the root, peel, lay the halves flat and keep the root on. Then cut in the direction the recipe needs: lengthwise and across for dice, across the grain for half-moons, with the grain for strips.
How do you cut an onion in slices or rings?
Lay a peeled half flat side down and slice across it for half-moons. For full rings, leave the onion whole, trim both ends, lay it on its side and slice straight across with a long, tall-bladed knife.
How do you cut an onion into strips?
Halve and peel the onion, then slice each half from the stem end towards the root, following the grain. Cut the root off last. These are the strips for fajitas, stir-fries and caramelised onions.
How do you cut an onion for burgers?
For rings, trim both ends of a whole peeled onion, lay it on its side and slice 2–3 mm thick. For a softer bite, cut thin half-moons instead and soak them in cold water for 10 minutes to tame the raw heat.
How do you cut an onion for fajitas?
Cut strips with the grain, about 5 mm wide. They stay in one piece during a hot, fast fry instead of collapsing into mush.
How do you cut an onion for kebabs?
Halve and peel the onion with the root left on, cut each half into three or four wedges, then split the wedges into pieces two or three layers thick. They stay flat enough to skewer and don't burn as fast as single layers.
How do you store an onion once it's cut?
Wrap the cut half tightly or seal it in a container, refrigerate and use it within a few days. Diced onion can be frozen flat on a tray and bagged for cooking later.
What is the best type of knife to cut onions?
A sharp chef's knife or santoku with a blade taller than your knuckles is the best all-rounder. If you cut vegetables all day, a nakiri's straight edge gives the cleanest slices. A paring knife is only for peeling and trimming.