Shelf spacing calculator
Evenly spaced shelves look right and use the height best — but the arithmetic has to allow for the thickness of every shelf, which is where a tape measure and a pencil usually go wrong by a few centimetres at the top.
How the gap is worked out
Take the thickness of all the shelves off the inside height and share what is left between the gaps — there is always one gap more than there are shelves. The first shelf sits one gap above the bottom; each next one is one gap and one shelf higher. The calculator gives those heights to the underside of each shelf, where the pins or the fixing go.
Typical gaps
| What goes on the shelf | Gap to allow |
|---|---|
| Paperbacks | about 230 mm |
| Most books | about 280 mm |
| Files, records, large books | about 350 mm |
| Shoes | about 180 mm; more for boots |
| Pantry jars and tins | about 300 mm |
| Towels and bed linen | about 350 mm |
Measure what you ownThese are starting points, not rules. Stand your tallest book or jar on the bench and add a finger’s width to lift it out.
Fixed or adjustable shelves
Adjustable on pins
- Drill two 32 mm rows of holes up each side
- The spacing can change when the contents do
- The shelf is 2 mm shorter than the gap between the sides
- Pin rows can be drilled on a CNC from the optimiser
Fixed
- Glued, doweled or screwed between the sides
- Stiffens a tall carcass — use one near the middle
- Needs the exact width between the sides
- The heights from this calculator are where the fixings go
Then check the span and cut the shelves
A long, loaded shelf bows: 800 mm of 18 mm MDF under books sags visibly. Check it with the shelf sag calculator before cutting, then open the shelves in the optimiser with the rest of the carcass — or build the whole list with the bookcase or wardrobe calculator.
Questions
Is the height measured inside or outside?
Inside: from the top of the bottom panel to the underside of the top. For a bookcase of 18 mm board that is the outside height less 36 mm.
Where do I measure each shelf from?
The heights are to the underside of each shelf, up from the bottom panel — where the pins sit.
Can the gaps be different?
Yes, but this calculator makes them equal. For a tall gap at the bottom, work out that shelf first and space the rest above it.
What about the 32 mm hole rows?
Pins go in the hole nearest each height; on a 32 mm row no shelf is ever more than 16 mm from where it was planned.
Plan your cut list now
Free, in the browser, with no account. Layouts, edging totals and machine files from one list.