How to Dice an Onion into Even Pieces

To dice an onion, halve it through the root, peel it and rest one half on its broad cut face. Make evenly spaced lengthwise cuts while leaving the root connection intact, then turn the onion and slice across those cuts. This straightforward method uses the onion's layers to produce small pieces for everyday cooking. Aim for a similar size throughout, rather than perfect cubes from a curved vegetable.

Choose the size and set up the board

Read the recipe before starting. A fine dice suits a preparation where you want small pieces distributed through each spoonful; a larger dice leaves more noticeable pieces. A rough chop allows more variation, while a mince is much finer. If the recipe specifies a size, follow it. Otherwise, choose a manageable spacing and keep it consistent across both halves.

A sharp chef's knife, gyuto or suitable santoku can handle an ordinary onion. Choose one that comfortably reaches through the half without requiring awkward repositioning. You do not need a dedicated onion knife. Our santoku versus gyuto comparison helps with the broader choice of an everyday prep blade.

Use a secure cutting board with clear space for the onion and a bowl for finished pieces. Remove loose peel from the working area before making fine cuts. Keep the supporting hand's fingertips curled back, with the thumb clear of the cutting path. Pause before moving the onion or changing your grip; speed is not the objective. Our bench scraper guide explains how to gather the finished pieces and move them into a nearby bowl.

Make a stable half and keep the root connection

Identify the stem end and the root end, which has the root fibres attached. Trim the stem end to make a flat surface, stand the onion on that surface and cut down through the centre of the root to divide it in half. Peel away the papery skin. Keep the root connection on each half so the layers remain joined during the next cuts.

Lay one half with its broad cut face firmly on the board. The root-to-stem direction now runs along the board. Work on one half at a time and move the other aside. If a loose outer layer prevents the half from sitting steadily, remove it rather than attempting to hold a rocking piece still with extra pressure.

Cut lengthwise, then across

With the root pointing away from you, make a series of parallel lengthwise slices down through the onion to the board, stopping short of the root connection. Keep the gaps between cuts similar. Use controlled slicing strokes appropriate to your knife, keeping the supporting hand clear; do not drive the blade horizontally toward that hand.

Stop and turn the onion a quarter turn on the board, keeping the flat face down. Starting at the stem side, slice down across the first cuts, advancing toward the root. Use spacing close to that of the first cuts. Small pieces should separate as you work. Stop while there is still enough onion to hold comfortably, and set the root end aside.

This method does not need an additional horizontal knife pass through the onion half. Its natural layers provide separation, although the curved outer sections and thicker layers can leave some larger pieces. Lay those pieces securely on the board and reduce them individually if your recipe needs a finer result.

Adjust a fine dice without turning it into mince

For smaller pieces, reduce the spacing in both directions. Tight crosscuts alone will leave longer pieces if the first cuts were widely spaced. Check a small handful before cutting the second half, then adjust the next cuts. Avoid repeatedly chopping the whole finished pile when only a few pieces are too large.

An onion's attached layers make this preparation different from cutting a solid carrot into planks. For long vegetable strips instead of small pieces, follow our julienne vegetables guide. After preparation, wash and dry the knife promptly and protect its edge in storage; our Japanese knife care guide covers that routine.