How to Calculate Wall Panelling Spacing in mm
By the developer of BattenCalc · Last updated October 17, 2026
Short answer: Decide how many panels or gaps you want, not how wide they should be. Then take the total width of all the strips off the wall width and divide what's left equally. For box panels: panel width = (wall − (panels + 1) × gap) ÷ panels. A 3,600 mm wall with four panels and 100 mm gaps gives 775 mm panels.
That covers one flat wall measured in millimetres, which is how most UK panelling is sold and set out. It works for shaker boxes, picture-frame moulding and vertical battens (board and batten). Sloping stair walls, chimney breasts and walls with sockets need the extra checks covered below.
Two kinds of panelling, two versions of the same sum
Wall panelling layouts come in two families, and the spacing question is phrased differently for each:
- Box panelling (shaker, picture-frame or "Georgian" boxes): you choose the gap between boxes and the number of boxes, then solve for the box width.
- Batten panelling (vertical strips straight onto the wall, sometimes called board and batten): you choose the strip width and roughly how far apart you want the strips, then solve for the exact gap.
Underneath, both are the same equation. The wall width equals the sum of all the openings plus the sum of all the strips. Doors2Floors' panelling guide says the same: write it as a simple sum and solve for the panel width once the strip width is fixed by the moulding you've bought.
Box panels: the formula
Wall Panel Planner explains the rule to remember: a wall has one more gap than panels. Four panels means five gaps, one at each edge and one between each pair.
panel width = (W − (n + 1) × g) ÷ n
- W = wall width (mm)
- n = number of panels
- g = gap between panels, which is also the gap at each end
Worked example: 3,600 mm wall, 100 mm gaps
- Four panels: (3,600 − 5 × 100) ÷ 4 = 3,100 ÷ 4 = 775 mm
- Five panels: (3,600 − 6 × 100) ÷ 5 = 3,000 ÷ 5 = 600 mm
Both work mathematically. Pick the one that looks better on the wall and around anything fixed to it.
How big should the gap be?
There is no standard. Wall Panel Planner calls about 100 mm the safe default in UK rooms, with anything from 80 to 120 mm looking considered. It also suggests three to five panels for most walls. Treat those as one publisher's design suggestions, not rules. What matters more is consistency: the same gap at the edges, between panels, and above and below the boxes.
Box height under a dado rail
The vertical sum is the same. For a single row of boxes under a dado rail:
box height = (dado rail underside − skirting top) − 2 × g
Suppose the underside of your dado rail sits at 900 mm and your skirting is 120 mm tall: (900 − 120) − 2 × 100 = 580 mm boxes. Doors2Floors puts dado panelling at roughly a third of the wall height, which on a typical 2.4 m UK ceiling means a capping rail at about 800–900 mm. The wainscoting height guide covers height in more detail.
Battens: the formula
For vertical battens, you choose the strip width and a target gap, then let the wall set the exact gap:
gaps (k) = round( (W − 2e + b) ÷ (target + b) )
gap = (W − 2e − (k − 1) × b) ÷ k
- b = batten width (mm)
- e = width of the batten at each end (usually b; 0 if the corners already have a strip)
Worked example: 3,000 mm wall, 70 mm battens, about 400 mm apart
Use your own batten width. MDF strip widths vary by supplier, so measure the strips you've bought. This example assumes 70 mm.
- k = round((3,000 − 140 + 70) ÷ (400 + 70)) = round(2,930 ÷ 470) = round(6.23) = 6 gaps
- gap = (3,000 − 140 − 5 × 70) ÷ 6 = 2,510 ÷ 6 = 418.3 mm
- Battens: 5 in the middle + 2 at the ends = 7
Measured from the left end of the wall, the left edges of the five middle battens fall at 488.3, 976.7, 1,465.0, 1,953.3 and 2,441.7 mm. Their centrelines are 35 mm further on: 523.3, 1,011.7, 1,500.0, 1,988.3 and 2,476.7 mm. The last end batten starts at 2,930 mm and finishes exactly at 3,000 mm.
In practice you'll mark to the nearest millimetre. Measure every mark from the same end of the wall. If you add 418 mm and 70 mm repeatedly, the rounding builds up across the wall.
| Wall width | 70 mm battens, ~400 mm target | Exact gap | Battens |
|---|---|---|---|
| 2,400 mm | 5 gaps | 396.0 mm | 6 |
| 3,000 mm | 6 gaps | 418.3 mm | 7 |
| 3,600 mm | 8 gaps | 371.2 mm | 9 |
| 4,200 mm | 9 gaps | 388.9 mm | 10 |
Setting out: what to do before you fix anything
The arithmetic is the easy part. Doors2Floors' setting-out advice is where most of the finished look comes from:
- Measure the wall in three places: at skirting height, at capping height and near the ceiling. UK walls are rarely parallel, and the worst case tells you where the tolerance has to go.
- Decide the panel count, not the panel width. Divide by a target width, round to a whole number, then recalculate. Equal panels of an odd size look better than equal panels plus one narrow one.
- Set out from the feature, not the corner. On a chimney breast wall, centre the layout on the breast and let the corners take the difference.
- Check sockets and switches. A stile that clips a faceplate is hard to finish. Change the panel count until sockets sit cleanly inside a panel. Moving a socket is a job for a qualified electrician.
- Pencil every line on the wall and look at it before cutting. Changing a pencil line is free.
- Work from one level line, not from the floor or skirting, which are rarely level.
On a staircase, Doors2Floors notes that the top rail should follow the pitch of the stairs while the stiles stay vertical. Wall Panel Planner's equal-gap formula assumes a rectangular wall, so treat a stair wall as a separate job.
Converting between mm and inches
US guides and timber labels are in inches, and a lot of online advice mixes the two. One inch is exactly 25.4 mm. A US "1x4" board is not 4 inches wide. Under the American Softwood Lumber Standard it dresses to 3/4 × 3 1/2 inches, or 19 × 89 mm. A 1x3 is 19 × 64 mm and a 1x6 is 19 × 140 mm. If you're following an American tutorial with UK materials, rerun the sums with your actual strip width rather than converting their answer.
Run your wall in millimetres
For a single wall, a phone calculator and the formulas above are enough. If you'd rather try several panel counts and see the result drawn to scale, both BattenCalc tools switch to millimetres. The free board and batten calculator handles vertical battens and gives every left-edge and centreline mark. The free wainscoting calculator handles box panels. Enter your gap as the stile width (and as the top and bottom rail if you want the same gap above and below), and it returns equal panel widths, the box height under your dado line, and a cut list for 45° frame pieces. For choosing the gap itself in a batten layout, see how far apart board and batten should be.
How we calculate
Box panels use n openings and n + 1 equal gaps: (W − (n + 1)g) ÷ n, which is the same as our stile formula with the gap as the stile width. Battens use k equal clear gaps between two end battens. Millimetre results use 25.4 mm per inch with full precision underneath. Openings such as doors, windows and sockets are not subtracted automatically. See methods and sources.
FAQ
How do you calculate wall panelling spacing?
Choose the number of panels and the gap. Multiply the gap by panels + 1, subtract that from the wall width, and divide the rest by the number of panels. For example, (2,400 − 5 × 100) ÷ 4 = 475 mm panels.
What is the standard gap between wall panels?
There is no official standard. Wall Panel Planner suggests about 100 mm as a safe default for UK rooms, with 80–120 mm looking considered. Keeping the gap identical at the edges, between panels, and above and below matters more than the exact figure.
How many panels should I put on my wall?
Wall Panel Planner suggests three to five for most walls. Fewer, wider panels feel calmer; more, narrower ones feel busier. Pick a count that keeps sockets and switches inside panels and frames any central feature, such as a bed or chimney breast.
How do you work out the gaps between battens?
Subtract the total width of all battens from the wall width, then divide by the number of gaps (battens − 1 when there's a batten at each end). Seven 70 mm battens on a 3,000 mm wall leave 2,510 mm, or six gaps of 418.3 mm.
What height should dado panelling be?
Doors2Floors suggests roughly a third of the wall height. That's about 800–900 mm on a standard 2.4 m ceiling, rising toward 1,000 mm on a 3 m Victorian wall. Line it up with a window board or picture rail if the room has one.
Should the edge gaps match the gaps between panels?
Usually, yes. Equal gaps everywhere is the classic layout and the one these formulas assume. If the wall has sockets, radiators or a feature you need to frame, you can widen the edge gaps deliberately, but keep both ends the same.
Sources
- Wall Panel Planner, Wall Panel Spacing Calculator (one more gap than panels, 100 mm default, 80–120 mm, 3–5 panels).
- Doors2Floors, Wall Panelling: How to Measure, Fit and Style It (setting out, measuring in three places, rule of thirds in mm, sockets, stairs).
- NIST, PS 20, American Softwood Lumber Standard (actual sizes in inches and mm).