About this calculator
This calculator works out the tongue-and-groove timber lining for one wall or ceiling, inside or outside: how many boards to buy and how to cut them, the battens and counter-battens behind them, and the fixings.
Enter the surface, its openings with their real position, the board's cover width (what one board covers once the tongue sits in the groove — not its nominal width) and the length the boards are sold in. The boards are laid row by row the way a carpenter lays them: an opening splits the rows it crosses; where a row is longer than one board the joint is made on a batten, never in line with a joint in the row below, and never leaving a piece shorter than the batten spacing; offcuts long enough are used in later rows. The pieces are then nested into whole boards, and the cutting plan shows which piece comes from which board. If your boards are sold in packs by area, switch to pack mode.
Formula
rows = ceil(cross dimension / cover width)
last row = cross dimension − (rows − 1) × cover width (ripped)
battens = at 0, s, 2s, … and at the far edge (no gap > s)
laying each row, from its start:
1. an offcut that finishes the row, if there is one
2. if more than one board is still needed: an offcut reaching a batten
that is a legal joint
3. else a new board — the rest of the row if it fits, otherwise up to the
farthest legal joint within one board length
legal joint: on a batten, not a joint of the row below, leaving pieces of
at least one batten spacing on both sides
boards = first-fit-decreasing nesting of the pieces + waste (as extra length)
packs (by area) = ceil(area × (1 + waste %) / cover per pack)
fixings = Σ battens under each piece × fixings per crossing
counter-battens = at 0, s', 2s', … and at the far edge, across the battens
The cross dimension is the height for horizontal boards and the length for vertical boards; battens always run across the boards.
Worked example
A 4 m wide strip of four rows, horizontal boards sold 3000 mm long, battens at 600 mm (0, 600, …, 3600, 4000), no waste:
row 1: new board to the batten at 3000; new board for the last 1000 → offcut 2000
row 2: the 2000 offcut reaches 1800 (3000 is row 1's joint); new board for 2200 → offcut 800
row 3: the 800 offcut reaches 600; new board 600 → 3000 (offcut 600); new board for 1000 → offcut 2000
row 4: the 2000 offcut reaches 1800 (600 is row 3's joint); new board for 2200
pieces 3000, 1000 | 1800, 2200 | 600, 2400, 1000 | 1800, 2200 = 16 m, 5 joints
boards: 3000 | 2400+600 | 2200 | 2200 | 1800+1000 | 1800+1000 → 6 boards (16 / 3 = 5.3)
The default 4 × 2.5 m wall (29 rows, 116 m of board) comes to 41 boards without waste and 45 with the 10 % waste.
FAQ
What is the cover width? The width one board adds to the surface: the full width minus the tongue. A 14 × 95 mm profile covers about 88 mm (one retailer lists 11.4 m of board per m²: 1000 / 11.4 ≈ 88 mm). Measure it on your boards if in doubt.
Why are joints placed on battens and staggered? A butt joint between battens has nothing to fix to, and joints in line from row to row make a visible seam and a weak line. So a board is cut back to a batten, the next row's joint goes on a different batten, and no piece is shorter than the batten spacing (a 100 mm stub cannot be fixed properly).
What batten spacing should I use? It depends on the board thickness and the manufacturer's instructions; the 600 mm default is a placeholder, not a recommendation. Thin boards and ceilings usually need closer battens.
Do I need counter-battens? Outside, the boards need a ventilated gap behind them. With horizontal boards the vertical battens leave the gap open; with vertical boards the horizontal battens would block it, so counter-battens go behind them.
Which standard applies? None is cited. EN 14519 and EN 14915 are product standards for profiled boards and timber cladding; neither gives a layout or take-off method.
Assumptions and limits
No standard is cited: the layout is geometry and counting.
Defaults to replace: the 14 × 95 mm board with 88 mm cover is from a Nordic retailer's listing; 3 m is a length Lithuanian stores list for interior lining boards; the 8-board pack, batten spacing and size, 3 m batten lengths, fixings per crossing and per pack and the 10 % waste are placeholders.
Layout: rows start at the bottom (horizontal boards) or the left edge (vertical boards); the last row is ripped. The laying is a good practical sequence, not a proven optimum. Battens run full length behind openings and no extra battens are added around openings, corners or edges. Boards cut back at an opening are still counted as full-width pieces. The structure behind the battens, the vapour barrier and trims are not counted. Spans and fixing strength are not checked.