The Easiest Way to Cut an Onion Into Even Pieces

For a simple onion dice, halve the onion through its root, peel it, and leave the root attached while making lengthwise cuts. Crosswise cuts then release the pieces. The root acts as a temporary handle that keeps the layers together. A stable board and curled fingertips matter more than cutting quickly.

Set up safely

Use a sharp chef’s knife, a steady cutting board, and a bowl for the diced onion. A dull knife needs more force and can slip. If the board moves, place a damp towel underneath. Keep your knife hand dry and work at a pace you can control.

1. Halve through the root

Trim the dry stem end, leaving the root in place. Cut the onion in half lengthwise through the root and peel away the papery skin. Remove any damaged outer layer. Each half should now have a flat side that can sit securely on the board.

2. Place flat-side down

Set one half on its cut face. Position it so you can make cuts along its length without your fingers being in the blade’s path. Curl fingertips into a claw and use the knuckles as a guide, keeping the thumb tucked back.

3. Make lengthwise cuts

Slice at regular intervals from the stem side toward the root, stopping before cutting completely through the root end. Use closer spacing for a finer dice and wider spacing for larger chunks. Let the onion’s natural layers help divide the pieces.

4. Cut across

Turn the half if needed so you can slice crosswise comfortably. Make evenly spaced cuts across the first ones. Diced pieces fall away as you work toward the root. Stop before your holding hand is crowded against the knife, and discard or reserve the final root section.

5. Repeat and collect

Dice the second half in the same way. Move the pieces into the bowl with a bench scraper or the flat side of the knife, keeping fingers away from the edge. Avoid dragging the sharp cutting edge sideways across the board.

Do I need horizontal cuts?

For everyday cooking, you can usually skip them because the onion already has layers. Additional horizontal cuts are used in some techniques for a finer, more uniform dice, but they introduce extra knife handling. The simpler approach is a useful starting method.

Choose the size for the recipe

Small dice softens quickly in sauces and fillings. Larger pieces keep more texture in soups and roasting dishes. Consistency helps the pieces cook at the same rate; exact millimeter measurements are rarely necessary for home cooking.

Reducing tears

A sharp knife and reasonable ventilation can help. Chilling the onion briefly before cutting may also reduce irritation. Do not use a trick that compromises your view of the board or puts a flame beside loose towels. If your eyes sting, pause and move away rather than cutting through blurred vision.

Common problems

If layers fall apart early, you may have cut through the root. If the onion rocks, check that it is resting on its flat face. If the dice is uneven, slow down and keep the two sets of cuts consistently spaced.

Storage and using scraps

Refrigerate diced onion in a covered container and use promptly, keeping it away from ready-to-eat foods if the outside of the onion or board was dirty. Clean sound trimmings can go into stock. Do not use moldy or decaying scraps.

Can I use a food processor?

Yes, but short pulses give more control. Continuous processing can turn an onion into wet purée rather than distinct pieces. A knife is often easier to clean for a single onion.