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A7 · Woodworking calculator

Shelf Spacing Calculator

Lay out equal visible openings inside a cabinet or bookcase, then compare each exact shelf-support mark with the nearest hole on a 32 mm drilling pitch. The schedule shows how far each shelf would move if you use the nearest hole.

Free to use · no account needed · calculations stay in this browser · formula reviewed 4 September 2026

Enter the clear cabinet opening

Measure the finished internal height and actual shelf thickness. Marks are measured upward from the inside base to the underside of each shelf.

mm
mm
Drilling comparison
mm

Equal clear opening = (interior height − total shelf thickness) ÷ (shelf count + 1). Exact underside marks accumulate one clear opening plus each preceding shelf. Optional hole marks round to the nearest 32 mm position from the entered first-hole height.

Example result using the values shown

Equal clear opening
211.5 mm
Clear openings
4
First shelf underside height
211.5 mm
Last shelf underside height
670.5 mm
ShelfExact undersideNearest 32 mm holeMove shelf by
1211.5 mm224 mm+12.5 mm
2441 mm448 mm+7 mm
3670.5 mm672 mm+1.5 mm

The exact schedule keeps equal clear openings. A 32 mm hole changes that shelf position by the shown shift.

  • 900 mm finished interior; three shelves at 18 mm.
  • 32 mm pitch begins at a 0 mm datum; pin line supports the shelf underside.

Exact spacing and drilling pitch are different answers

Equal openings often land between system holes. This calculator preserves the exact layout, then shows the nearest 32 mm alternative and how far each shelf would move. Using those rounded hole positions may make the clear openings slightly unequal.

This schedule does not calculate shelf load, sag or whether the chosen supports are suitable.

The schedule locates shelf undersides only. Confirm pin diameter, front/back rows, the first-hole position, fixed shelves, face-frame interference and the hardware maker's instructions.

Blank shelf check

Finished interior_____ mm
Shelves_____ × _____ mm
First-hole height / pitch_____ / 32 mm
First and last support_____ / _____ mm