Standard cabinet widths and the 3-inch increment rule

The increment exists because kitchens are laid out in whole feet and cabinets have to fill runs without custom work. Three inches divides evenly into 12, so any run that is a whole number of feet can be filled from stock widths, and a filler strip covers the remainder when a wall is out of square or a run lands awkwardly.

It also keeps inventory sane. A manufacturer offering every width in one-inch steps would carry three times the SKUs for a benefit almost nobody needs, because the fillers absorb the difference invisibly once the doors are on.

The practical consequence for anyone building rather than buying: you do not need to design widths. Pick from the ladder, add fillers where the run does not close, and the cut list falls out of the width automatically.

Widths below 9 inches are usually spacers or fillers rather than cabinets. Above 36, single cabinets become awkward to hang and transport, so long runs are made from two boxes.

This is the part that makes the increment useful. For a frameless box in ¾" (18 mm) sheet material with the sides running full height, every horizontal part is the nominal width minus two side thicknesses: W − 1½".

So a 30" base cabinet has a 28½" bottom deck, 28½" stretchers, and a 28½" back. A 24" has 22½". A 36" has 34½". The sides never change with width - only with depth and height - so a whole cabinet line shares one gable size per type.

Face-frame construction shifts the arithmetic but not the principle: the box is typically built to the nominal width less the frame overhang, and the frame itself is made to nominal width. Pick one convention, write it at the top of the spreadsheet, and never mix the two in one job.

European and most Commonwealth cabinet lines do not use 3-inch steps. They step in 150 mm: 150, 300, 450, 600, 750, 900, 1000 and 1200 mm, with 600 mm as the workhorse width the way 24" is in North America.

The arithmetic is the same shape. For an 18 mm frameless carcass, horizontal parts are W − 36 mm, so a 600 mm cabinet has 564 mm decks and stretchers. Standard depths are 560-580 mm for base and 300-350 mm for wall units, with 720 mm as the standard carcass height on a separate 150 mm plinth.

Mixing the two systems in one job is where cut lists go wrong. 600 mm is 23⅝", not 24", and that ⅜" turns up as a gap at the end of the run.

Because every part is a fixed offset from the nominal width, a whole cabinet line is one small table with a formula in each column rather than a drawing per cabinet.

Export that table as CSV or XLSX and import it straight into the sheet optimizer - the free tier accepts up to 5 rows, which covers a full kitchen comfortably. The optimizer then nests the parts and returns sheet counts you can order from.