Equal shelf spacing starts after board thickness, not before.
This calculator divides one clear inside height into a chosen number of storage openings. It first subtracts the thickness of every internal shelf board, then divides only the height that remains. That order matters: dividing the cabinet height first and adding shelves afterward makes every finished opening smaller than the number on the sketch.
The result also tests a real object rather than treating equal spacing as the goal by itself. Enter the tallest item and the extra handling space you want above it. RoomFact reports whether every equal bay can hold that target and gives underside marks measured from the inside bottom, so the arithmetic becomes a checkable layout rather than a single unexplained gap.
Worked example
Five openings inside a 180 cm cabinet
A cabinet has 180 cm of clear inside height. Four internal shelves, each 1.9 cm thick, will create five equal openings. The tallest book is 30 cm and the owner wants 2.5 cm above it.
Clear inside height
180 cm
Clear openings
5
Shelf-board thickness
1.9 cm
Object plus headroom
32.5 cm
How RoomFact reads it
Four boards use 7.6 cm, leaving 172.4 cm for the openings. Dividing that remainder by five creates 34.5 cm clear bays. The shelf undersides land about 34.5, 70.9, 107.2, and 143.6 cm above the inside bottom.
Each opening leaves about 4.5 cm above the 30 cm book, which exceeds the selected 2.5 cm headroom by roughly 2 cm.
The marks identify shelf undersides, not shelf tops or pin-hole centres. Changing that reference during installation creates a repeated error.
An adjustable pin system may not contain a hole at every calculated mark. Snap to the real hole row, then measure the resulting bays instead of assuming they remained equal.
01
Measure the space the objects can actually use
Measure from the top face of the cabinet bottom to the underside of the cabinet top. Do not use the outside case height, include a plinth, or count the thickness of the top and bottom twice. Take the measurement at the front and back when the case may be out of square, and use the smaller relevant value for the first layout.
Measure one real shelf board with its finished edge treatment. Nominal material descriptions can differ from finished thickness, and a small difference repeats through every internal shelf. If shelf supports lift the board above their hole centre, use the board underside as the mark and follow the hardware instructions for the hole position.
02
Count openings, not boards
An opening is a clear storage bay. One open cabinet has one opening and no internal shelf. Two openings require one internal shelf; five openings require four. The calculator makes that relationship explicit so an entered count cannot silently consume one extra board thickness.
Equal spacing is useful for a calm elevation and repeated storage, but it is not automatically the most efficient plan. List the object groups first. A tall appliance, record sleeve, art book, or display piece can justify one intentionally tall bay while smaller objects share the remainder.
03
Use the tallest object as a pass-or-change test
Measure the object in its stored orientation and include a lid, handle, book jacket, basket rim, or cable bend that occupies vertical space. Then choose headroom for the way the object is removed. A closely packed row of books may need finger space; a light display object may need visual space; a heavy appliance may need enough room for a safe grip.
When the target fails, change one variable at a time. Fewer openings usually creates the largest gain. Thinner boards recover only the difference multiplied by the number of internal shelves, and they can reduce stiffness or load capacity. A mixed-height layout can be better than forcing every object into equal bays.
04
Separate vertical layout from structural approval
Common cabinet systems and drilling jigs use repeated shelf-pin rows, including 32 mm increments, but the exact hole size, setback, first-hole location, and support geometry belong to the selected hardware. Use the calculator marks as target undersides, then translate them through the jig or manufacturer instructions. Never drill from an assumed universal datum.
Spacing does not prove that a shelf can carry the planned load. Board material, unsupported span, depth, edge construction, moisture, fasteners, and support hardware all affect deflection and failure. Confirm the product load information or use a qualified design method, keep heavy objects low, and secure applicable storage furniture to the wall according to its instructions.