How to Dice an Onion
A properly diced onion has pieces close enough in size that they cook at the same rate, whether that's soft and translucent in a sauce base or crisp-edged in a salsa. The trick is cutting with the root end intact until the very last step, since that's what holds the layers together while you make the earlier cuts.
Steps
- 1Trim off the stem end (the pointed top) but leave the root end attached.
- 2Peel off the papery skin and the first tough layer underneath.
- 3Cut the onion in half through the root, so each half has a flat side to sit on.
- 4Lay one half flat-side down and make horizontal cuts parallel to the board, from the outer edge toward the root, stopping about 1/2 inch (1 cm) before the root end so the layers stay connected.
- 5Make several vertical cuts down through the onion from the outer edge toward the root, again stopping just short of the root.
- 6Slice crosswise through the onion, perpendicular to the vertical cuts, to produce even dice. The size of these final cuts sets the size of the dice.
- 7Repeat with the second half, then discard the root ends.
Common mistakes
- Cutting through the root too early: this collapses the layers and turns clean dice into ragged, uneven scraps.
- Skipping the horizontal cuts: without them, the final crosswise slices produce long strips instead of cubes.
- Using a dull knife: it crushes the onion's cell walls instead of slicing them, which releases more of the compounds that cause eyes to sting.
- Cutting all the way through on the vertical cuts: leaving a hinge at the root is what keeps everything together until the last slice.
Equipment
- Sharp chef's knife
- Cutting board
FAQ
How small should the pieces be for a fine dice versus a regular dice?
For a fine dice, space the horizontal, vertical, and crosswise cuts about 1/8 inch (3 mm) apart. For a standard dice, space them about 1/4 to 1/2 inch (6-12 mm) apart.
Why does this method keep the onion from falling apart?
Leaving the root end uncut acts as a hinge holding all the layers together, so you can make multiple clean cuts before the onion separates into loose pieces.
Does chilling the onion first really reduce eye irritation?
Yes. Chilling the onion for 10-15 minutes before cutting slows the release of syn-propanethial-S-oxide, the volatile compound that irritates eyes, because the reaction that produces it is temperature-dependent.
Can this same technique be used for a red onion or shallot?
Yes, the root-end technique works the same way on red onions and shallots, though shallots are smaller and usually only need two or three horizontal and vertical cuts before slicing.
Need exact temperatures or timing? Check our Time & Temperature Guide →