Equal spacing· 3 min read
How to Space Shelves Evenly in a Cabinet or Bookcase
A cabinet with 1,800 mm inside height and 18 mm shelves: how to get equal openings for 3, 4 or 5 shelves, where each shelf goes and where to drill.
Splitting a cabinet into equal openings looks like simple division. The common mistake: you divide the height by the number of openings and forget the shelf thickness. With four 18 mm shelves that's 72 mm, which then goes missing from the top opening. The right way is to subtract the shelves first and divide what is left.
How it works
- 1Measure the inside height — from the top face of the bottom panel to the underside of the top. In the example, 1,800 mm (about 71 in).
- 2Subtract the thickness of all shelves. With 4 shelves of 18 mm: 1,800 − 72 = 1,728 mm.
- 3Divide the rest by the number of openings. Four shelves make five openings: 1,728 / 5 = 345.6 mm.
In the spacing calculator that means: length 1,800 mm, element width 18 mm, “I know how many” and at the ends “Same gap as between elements” — the opening at the bottom and at the top is as tall as the others.
How many shelves
| Shelves | Height of each opening | Centre to centre |
|---|---|---|
| 3 | 436.5 mm | 454.5 mm |
| 4 | 345.6 mm | 363.6 mm |
| 5 | 285 mm | 303 mm |
If you know how tall the things you'll store are, work the other way round with “Gap must not exceed”. With a 300 mm limit, the calculator returns 5 shelves with 285 mm openings — four shelves would leave openings taller than 300 mm.
Where the shelves go (4 shelves)
| Shelf | Underside from the bottom | Shelf centre |
|---|---|---|
| 1 | 345.6 mm | 354.6 mm |
| 2 | 709.2 mm | 718.2 mm |
| 3 | 1,072.8 mm | 1,081.8 mm |
| 4 | 1,436.4 mm | 1,445.4 mm |
For fixed shelves (dowels, screws) you mark the underside of each shelf. For a shelf on pins, the pin sits just below the underside, so drill the hole half a pin diameter lower.
Equal spacingOpen this example in the spacing calculatorTaller openings at the bottom and top
Sometimes you don't want all openings equal — you want room for a basket at the bottom and boxes at the top. Then choose “Fixed end space” at the ends. With 400 mm and 3 shelves, the bottom and top openings are 400 mm and the two middle ones 473 mm each. If you want different heights at the bottom and top, split the cabinet into two parts and work each one out separately.
Open shelving: shelves right to the ends
On open shelving without a separate bottom and top, the shelves themselves form the bottom and top surfaces. Then choose “Elements touch the ends”. Five shelves over 1,800 mm give four openings of 427.5 mm, with the shelves starting at 0, 445.5, 891, 1,336.5 and 1,782 mm.
System 32 and tenths of a millimetre
Many cabinets have a row of holes in the sides following the 32 mm system — 5 mm holes 32 mm apart centre to centre. In such a cabinet you can't put a shelf at exactly 345.6 mm; you pick the nearest hole and the error is at most 16 mm. It won't be noticeable as long as you follow the same rule for every shelf. If you drill yourself, you can go exactly by the numbers.
Workshop tips
- Mark every position from the bottom, not from the previous shelf, so errors don't add up.
- Transfer the same marks to both sides at once, for example with a straight stick marked as a story pole. The shelves won't end up sloping.
- Before measuring the inside height, check that the bottom and top of the cabinet are really parallel. Measure at the front and back, next to both sides.
- How much a shelf can carry depends on the material, thickness, span and support. For heavy loads (books, tools) follow the board and hardware manufacturer's data.