Small cabinet
900 mm inside height
2 shelves, 18 mm thick
3 openings of 288 mm
The practical toolbox
Shelf spacing calculator
Calculate equal shelf spacing for cabinets and bookcases. Allow for shelf thickness, check item fit and save a measured layout in millimetres or inches.
MeasurementsChoose your units. Costs, watts and time stay the same.
Save this version with its URL. Bookmark this page or copy its link to reopen your inputs later. Save a new link after making changes. Anyone with the link can read your inputs. Results are recalculated on reopening; print a copy if you need a fixed record.
Create a saved link with AI
Give your AI assistant your measurements or figures and the instructions below. It can create a ready-to-open link for this shelf spacing planner. Open the link, check the inputs, then bookmark it or copy the URL to reuse it later.
Copy this prompt and add your information:
Read https://www.lejnel.com/shelf-spacing-url-guide.txt and generate a clickable saved-plan URL for my shelf spacing planner. Convert my units to the guide’s required units. Ask for missing inputs instead of guessing, and explain any assumptions. Return the link and a summary of the inputs used.
Read the URL format and examples · AI instructions for all tools
The URL contains your inputs. Anyone with the link can read them. Future calculator updates may change results; retain a printed copy when you need a fixed record.
Equal openings & shelf positions
On a small screen, swipe the drawing or table sideways if needed. Match each shelf’s colour and number to its table row. All positions start at the cabinet floor.
| Shelf | Underside | Centre | Top |
|---|
How to calculate equal shelf spacing
Subtract the total shelf thickness from the cabinet’s inside height, then divide the remaining height by the number of openings. Adding three shelves creates four openings. Clear opening means the empty vertical space, not the distance between shelf centres.
For inside height H, shelf thickness T and shelf count N: clear opening = (H − N × T) ÷ (N + 1). Shelf k has underside height k × opening + (k − 1) × T, measured upwards from the cabinet floor. Add T/2 for its centre or T for its top.
How to measure a cabinet for shelves
- Measure the clear inside height, from the top of the cabinet floor to the underside of its top. Exclude the floor and top panel thicknesses.
- Measure the actual shelf board thickness. Use the same thickness for every added shelf in this plan.
- Count the shelves you want to add. Two shelves create three openings; three shelves create four.
- Optionally measure the tallest item and choose how much handling space you want above it.
- Read the numbered layout and mark every shelf from the same floor datum. Check hardware offsets before making any hole marks.
Shelf spacing examples
These examples use 18 mm shelves. Cabinet sizes and thicknesses are illustrative, not product specifications.
Medium cabinet
1,200 mm inside height
3 shelves, 18 mm thick
4 openings of 286.5 mm
Tall bookcase
1,800 mm inside height
4 shelves, 18 mm thick
5 openings of 345.6 mm
Worked example
A 1,200 mm inside height with three 18 mm shelves leaves 1,146 mm of empty space. Each of the four openings is 286.5 mm high. The shelf undersides are 286.5, 591 and 895.5 mm above the cabinet floor. A 250 mm item with 20 mm chosen clearance fits, with 16.5 mm to spare.
Is shelf spacing measured between centres or clear surfaces?
Clear spacing is the empty height available to an item. The distance from one shelf centre to the next includes one shelf thickness. This calculator reports equal clear openings and separately lists underside, centre and top positions.
How many shelves can fit my items?
Enter the item height and your chosen extra space. The result compares them with the clear opening and estimates the maximum shelf count, up to this planner’s limit of 30. A fit result concerns height only; it does not check width, depth or load capacity.
Should I mark the centre or underside?
The table gives all three references so you can use the one required by your support system. Shelf-pin holes are often offset from the shelf surface. Read the support instructions and measure the actual hardware before translating this layout into hole marks.
Can I use an existing cabinet hole grid?
This planner calculates continuous equal spacing. It does not snap to a hole grid. Available holes may require unequal openings; compare their actual supported shelf heights with the suggested layout before drilling or moving shelves.
Can I use inches and save my plan?
Use the metric/imperial control to switch the displayed measurements without changing the physical layout. Copy the complete plan link to save your inputs or share them, and print the results for marking out. Anyone with that link can read its measurements.
What is not included?
Assumes a rectangular, level cabinet and identical horizontal shelves. Cabinet width is illustrative in the elevation. This is not a cutting list, structural design, load rating or fixing recommendation. Sag, wall anchorage, material strength, door hardware and installation tolerances are not evaluated. Measure the finished space and actual boards; displayed values are rounded, so mark from the common floor datum rather than adding rounded gaps. The drawing is not a full-size template. You are responsible for checking measurements and safe installation.
Related: equal hole spacing calculator · gallery wall planner.