To cut an onion, slice off the top (stem) end, halve it through the root, peel off the skin, then make horizontal and vertical cuts toward the root before slicing down across them to produce an even dice. Keeping the root intact holds the onion together while you cut, giving uniform pieces and safer control. A sharp chef knife and the claw grip make it quick. This guide explains how to cut an onion step by step, including how to dice it finely.

Quick Answer

Cut off the stem end, halve through the root, peel, then make horizontal and vertical cuts toward the (intact) root and slice down across them to dice. The root holds the onion together for even, safe cutting.

What You Need

How to Cut an Onion: Steps

  1. Cut off the top (stem) end, leaving the root end intact.
  2. Stand the onion on the cut end and halve it through the root.
  3. Peel off the papery skin from each half.
  4. Place a half flat-side down. Make horizontal cuts parallel to the board toward, but not through, the root.
  5. Make vertical cuts down through the onion, again stopping at the root.
  6. Slice down across these cuts to release an even dice.
  7. Discard the root end.

Key Takeaway: Leave the root on until the end. It is the hinge that holds all the layers together, so your cuts stay even and your fingers stay clear. Cutting the root off first makes the onion fall apart and slip.

For a Finer or Coarser Dice

Make your horizontal and vertical cuts closer together for a fine dice, or wider apart for a coarse one. The spacing of the cuts controls the size of the pieces.

How to Reduce Crying

  • Use a sharp knife, which damages fewer cells and releases less irritant.
  • Chill the onion before cutting.
  • Cut near good ventilation or a running extractor fan.
  • Cut the root end last, as it holds the most of the compound that stings.

Safety Notes

  • Use the claw grip to protect your fingertips.
  • Keep the onion flat-side down for stability.
  • Use a sharp knife; dull knives slip on the skin.
  • Cut on a stable board.

FAQ

How do you cut an onion?

Cut off the stem end, halve through the root, peel, then make horizontal and vertical cuts toward the intact root and slice down across them to dice.

Why leave the root on when cutting an onion?

The root holds the layers together so your cuts stay even and the onion does not fall apart, which is safer and gives a more uniform dice.

How do you stop crying when cutting onions?

Use a sharp knife, chill the onion first, cut near ventilation, and leave the root (which holds the most irritant) until last.

Bottom Line

Cut an onion by halving it through the intact root, peeling, then making horizontal and vertical cuts before slicing across to dice. The root keeps it together for even, safe cutting. Use a sharp knife and the claw grip. See our best chef knives and how to hold a chef knife guides.

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