Board-and-batten planner · Formula 1.0

Board-and-batten spacing calculator

Plan equal board-and-batten spacing for one rectangular usable wall. Compare flush outer battens with equal edge gaps, then get clear gaps, centre-to-centre (center-to-center) spacing, marks from one datum, and aggregate vertical material in metric or imperial units.

Measurement system

Metric accepts mm, cm, and m. Imperial accepts inches, fractions, and feet plus inches. Valid calculated values convert when you switch; unfinished entries are kept separately so unchanged digits are never silently relabelled.

The finished horizontal span between the two edges that define this layout. Deduct side trim only when it sits outside the planned design.

Measure between the left and right layout edges. Detailed measurement steps appear below the calculator.

The cut length of one vertical batten, measured between its real lower and upper edges.

Use the planned cut length of each vertical batten.

Measure the face visible on the wall. Nominal product sizes can differ from the installed face width and will change every gap.

Measure the visible face; do not rely on a nominal size.

Count every vertical piece in this uninterrupted span, including outer battens when the flush-edge layout is selected.

Enter a whole number from 1 to 200.

How should the layout meet the wall edges?
Adds a percentage to total vertical material only. It does not calculate stock lengths, cuts, defects, or reusable offcuts.

Defaults to 10%. It applies only to aggregate vertical length.

Preview and result

Enter one usable wall

The valid result will show the practical clear gap first, followed by calculated values, a proportional diagram, positions from the left datum, and aggregate material length.

Example of the layout diagram An example wall with four vertical battens, a usable-width dimension line, and the left wall edge marked as the zero datum. It is not a calculated result. 1 2 3 4 usable wall width 0 · left datum
Illustrative example only. Your proportional drawing appears after a valid calculation.

No layout has been calculated yet.

Measurement guidance

Define the rectangle and its datum

Use finished surfaces, not rough dimensions. Decide whether existing side trim sits outside the design. If it does, measure between that trim. If the outer battens form the design edges, include their full face width and select flush edge battens.

Check width near the top, middle, and bottom of the planned span. Different readings mean the wall is not represented perfectly by one rectangle; investigate the difference and decide how the real installation will resolve it before accepting one usable width.

Use actual material dimensions

Measure the face that will remain visible after installation. Products described as battens, trim, moulding, or molding can use nominal names that are not the installed face width. A small width difference repeats across every batten and changes every calculated gap.

Measure the planned vertical cut height from its real lower edge to its real upper edge. Formula 1.0 assumes every vertical piece has that same height and face width.

Result interpretation

Use each spacing value for the right job

  • Clear gap: the visible open distance from one batten edge to the next.
  • Centre-to-centre: the distance between adjacent batten centre lines.
  • Left-edge position: the mark where the left face of each batten begins.
  • Centre position: an alternative centre-line mark for alignment or checking.

Read the schedule from one starting point

Every position is measured from the left usable-wall edge at zero. The first practical mark is not a command to add the rounded gap repeatedly; return to the datum for each mark so rounding does not accumulate across the wall.

Read material as aggregate length

Base aggregate is the number of vertical pieces multiplied by their height. Waste is shown separately. Neither value determines stock lengths, board quantities, cuts, or usable offcuts.

Transparent formula

How Formula 1.0 calculates equal spacing

Let W be usable width, H batten height, B actual batten width, N batten count, and A waste percentage. First find unoccupied width: R = W − N × B. A spacing layout is valid only when R is greater than zero.

  • Flush edge battens: G = R ÷ (N − 1), with at least two battens.
  • Equal edge gaps: G = R ÷ (N + 1).
  • Adjacent centre spacing: S = B + G.

Positions and material

Number battens from i = 0. A flush layout uses left positions Pᵢ = i × (B + G). An equal-edge layout uses Pᵢ = G + i × (B + G). Each centre is Cᵢ = Pᵢ + B ÷ 2.

Base vertical material is L = N × H. With waste it is LA = L × (1 + A ÷ 100). Calculations and SVG geometry retain unrounded normalized values; rounding happens only for display and site-friendly marks.

Worked examples

Reviewed Formula 1.0 layouts

These examples use the published formula inputs and outputs that are also covered by the automated Formula 1.0 fixtures. They are checks of the convention, not suggested dimensions for a real wall.

Metric · flush edge battens

For W = 3000 mm, H = 2400 mm, B = 65 mm, N = 6, and A = 10%, the battens occupy 390 mm. The remaining 2610 mm is divided across five gaps, giving a 522.0 mm clear gap and 587.0 mm centre spacing.

Left-edge marks are 0, 587, 1174, 1761, 2348, and 2935 mm. The final 65 mm batten closes at 3000 mm. Vertical material is 14.400 m before waste and 15.840 m with waste.

Metric · equal edge gaps

For W = 2400 mm, H = 2400 mm, B = 60 mm, N = 5, and no waste, 2100 mm remains for six gaps. Each clear gap is 350.0 mm and centre spacing is 410.0 mm.

Left-edge marks are 350, 760, 1170, 1580, and 1990 mm. Both edge gaps are 350 mm, and base aggregate vertical material is 12.000 m.

Imperial · flush edge battens

For W = 120 in, H = 96 in, B = 2.5 in, N = 6, and A = 10%, 105 in remains for five 1 ft 9 in (21 in) clear gaps. Centre spacing is 1 ft 11 1/2 in (23.5 in).

Left-edge marks are 0, 23.5, 47, 70.5, 94, and 117.5 in. Vertical material is 48 ft before waste and 52.8 ft with waste; the separate rounded-up planning total is 53 ft.

Precision and rounding

Round each mark from the datum

Metric calculated gaps and positions display to 0.1 mm, while practical marks round to 1 mm. Imperial calculated values display to 1/64 in, while practical marks round to 1/16 in. The calculator rounds each position independently from the left datum and never rounds intermediate formula values.

A practical schedule can therefore show adjacent rounded gaps that differ slightly even though the calculated gaps are equal. Use the calculated value to check the design and the independently rounded position marks to lay it out.

Set waste for the real purchase plan

The default 10% is an editable planning allowance, not a universal recommendation. Increase, reduce, or remove it based on actual stock lengths, end trimming, defects, grain or pattern matching, and whether offcuts can be reused.

Waste is applied after base aggregate length. The planning total rounds upward, but it remains a length estimate—not a stock count or optimized/optimised cut list.

Before installation

Common planning mistakes

  • Using nominal batten size instead of the actual visible face width.
  • Measuring wall-to-wall when side trim should sit outside the usable span.
  • Choosing flush battens when the design actually needs equal gaps at both edges.
  • Confusing the visible clear gap with centre-to-centre spacing.
  • Stepping off rounded gaps instead of marking every position from one datum.
  • Subtracting an internal opening as though it simply shortened one rectangular span.
  • Treating aggregate material length as a board count or optimized cut list.

Planning aid and safety limits

Formula 1.0 is a planning aid for identical vertical battens on one rectangular usable span. It does not inspect the substrate, select fixings, assess structure, detect concealed services, or determine code compliance. The proportional diagram is not a full-size template.

Verify site measurements, actual material sizes, wall conditions, manufacturer instructions, applicable codes, and qualified trade advice where relevant before buying, cutting, drilling, or fastening material.

Read how calculations and limitations are reviewed

Related planning

Planned, but not published as thin pages

Picture-frame moulding/molding, wainscoting, wood-slat spacing, cabinet hardware, tile layout, and genuine trim cut-list tools remain future ideas. They will become links only after each destination has a working tool, reviewed formula, useful visual, guidance, examples, and limitations.

Formula and page guidance last reviewed 3 August 2026.