Feather Edge Fence Calculator: Boards & Spacing

This calculator works out how many feather edge boards (also called waney edge or lap panels) you need for a fence run, plus the spacing between each board and the total linear metres of boards required. You enter the fence length, the board width, and the overlap you want between boards, and it returns the number of boards, the visible (gauge) spacing, and the total board length needed.

Formula

The core formula is simple: each feather edge board covers a width equal to its full board width minus the overlap with the neighbouring board. That covered width is called the gauge or lap spacing.

Number of boards = ceil( Fence length / Gauge )

Where:

• Fence length – the total horizontal run of the fence, in metres (or feet, if you convert consistently).
• Board width – the actual width of one feather edge board, typically 100–175 mm, in millimetres.
• Overlap – the amount one board covers the next, usually 20–40 mm, in millimetres.
• Gauge = Board width – Overlap, in millimetres. This is the visible width of each board from the front.
• Ceil() – round up to the next whole number, because you cannot buy a fraction of a board.

Total board length = Number of boards × Board width (converted to metres). This is the linear metres of timber you need to buy, assuming no waste from cutting.

Worked Example

Using the default values: fence length = 10 m, board width = 150 mm, overlap = 25 mm.

1. Gauge = 150 mm – 25 mm = 125 mm = 0.125 m.
2. Number of boards = 10 m ÷ 0.125 m = 80 boards exactly.
3. Since 80 is already a whole number, ceil(80) = 80 boards.
4. Total board length = 80 × 0.150 m = 12.0 m.

So for a 10-metre fence with 150 mm boards overlapped by 25 mm, you need 80 boards, each showing 125 mm of face, and you will buy 12 linear metres of board timber.

Why Feather Edge Fences Use Overlap

Feather edge boards are tapered – thicker at one edge (the butt) and thinner at the other (the feather). They are fixed vertically to horizontal rails (arris rails) with the thick edge overlapping the thin edge of the previous board. This creates a water-shedding surface: rain runs down the face and over each lap, rather than seeping between boards. The overlap is not just decorative – it is the waterproofing mechanism. Without it, you would have gaps that let wind and rain through, and the fence would look unfinished.

The overlap also allows for natural movement. Timber expands and contracts with humidity, and the lap gives a little room so boards do not buckle or split when they swell.

How to Choose the Overlap and Board Width

Your choice of overlap directly affects both the look and the cost. Common overlaps are 20 mm, 25 mm, and 30 mm.

• 20 mm overlap – uses more boards per metre, gives a tighter, more solid appearance, but costs more and reduces the visible width of each board.
• 25 mm overlap – a standard middle ground, works well with 125–150 mm boards.
• 30 mm overlap – fewer boards, more visible width per board, slightly less weatherproof but still adequate for most garden fences.

Board width is often dictated by what your local timber merchant stocks. Common widths are 100 mm, 125 mm, 150 mm, and 175 mm. Wider boards mean fewer boards to nail, but they are heavier and can be more prone to warping if not seasoned properly. A 150 mm board with a 25 mm overlap (gauge 125 mm) is a very typical combination for a 1.8 m high fence.

Common Mistakes and How to Avoid Them

The most frequent error is mixing units. Fence length is usually measured in metres, but board width and overlap are given in millimetres. Always convert the gauge to metres before dividing. In the example, 125 mm becomes 0.125 m – forgetting this gives you 80,000 boards instead of 80.

Another mistake is forgetting to round up. If your calculation gives 79.3 boards, you cannot buy 0.3 of a board – you need 80. The calculator does this automatically with the ceil function.

A third issue is not accounting for end posts and corner posts. The fence length should be the distance between the inside faces of the end posts, not the total distance including the posts. If you measure from outside edge to outside edge, you will overestimate by the width of two posts (typically 75–100 mm each).

Finally, do not forget waste. The formula assumes every board is used perfectly. In reality, you may need to cut a board to fit around a post, or a board may split during nailing. Adding 5–10% extra is standard practice, especially for first-time builders.

Cost and Material Considerations

While this calculator gives you the board count and linear metres, the actual cost depends on your local timber prices, which vary widely by region, wood type (pressure-treated softwood is common), and board grade. You can estimate cost by multiplying the total linear metres by the price per metre for the board you choose. Remember to add the cost of rails (usually 3 per fence panel height), posts, gravel boards, nails, and concrete – these are not included in this calculator.

Also consider that feather edge boards are sold by the linear metre, but some suppliers sell them in fixed lengths (e.g., 1.8 m, 2.4 m, 3.0 m). If your fence height is 1.8 m, you will cut each board to length, and the offcut may be usable for the next section if you plan carefully. Buying boards in lengths that match your fence height minimises waste.

Alternatives to Feather Edge

Feather edge is not the only fencing option. If you are comparing, here are the main alternatives:

• Closeboard fencing – essentially the same as feather edge; the terms are often used interchangeably. Some regions call it “overlap fencingâ€�.
• Palisade fencing – vertical boards with a pointed or flat top, fixed with a small gap or slight overlap. More decorative but less weatherproof unless overlapped.
• Panel fencing – pre-made panels (often 6 ft × 6 ft) with horizontal or vertical slats. Quicker to install but less durable than feather edge because panels are thinner and more prone to wind damage.
• Hit and miss fencing – boards fixed alternately on each side of the rails, leaving gaps for airflow. Good for wind reduction but not private.
• Trellis or lattice – decorative, not for privacy or security.

Feather edge is generally considered the most robust and long-lasting option for a boundary fence, especially in windy areas, because the overlapping boards create a solid barrier that resists wind pressure better than panels.

Frequently Asked Questions

How many feather edge boards do I need for a 20 metre fence?

Using the same defaults (150 mm board, 25 mm overlap), gauge is 125 mm = 0.125 m. 20 m ÷ 0.125 m = 160 boards exactly. If you use a 30 mm overlap, gauge is 120 mm = 0.12 m, giving 20 ÷ 0.12 = 166.67, so you would need 167 boards.

What is the standard overlap for feather edge fencing?

There is no single standard, but 25 mm is the most common overlap for boards in the 125–150 mm width range. For wider boards (175 mm), some builders use 30 mm to maintain a similar proportion. For narrower boards (100 mm), 20 mm is typical. The key is to keep the gauge (visible width) between 100 and 125 mm for a balanced look.

Can I use this calculator for a fence that is not a straight line?

No – this calculator assumes a straight, level run. If your fence has corners, curves, or steps, you need to measure each straight section separately and add the board counts together. For curves, you would need to measure along the curve (using a flexible tape) and accept that boards will need cutting at angles, increasing waste.

Do I need to include the posts in the fence length?

No. Measure the length between the inside faces of the two end posts (or between the inside faces of the posts at each corner). The boards are fixed to the rails that run between posts, so the rails span that distance. Including the posts would add about 150–200 mm per post, which is unnecessary and would give you too many boards.

What if my board width is not standard?

Most timber merchants sell feather edge in a few standard widths, but you may find odd sizes from reclaimed or imported timber. The calculator works for any width – just enter the actual width in millimetres. If you are cutting your own boards from wider stock, measure the final width after cutting.

Why does the calculator show total board length in metres, not in boards?

Because timber is sold by the linear metre, not by the board. Knowing the total linear metres lets you compare prices directly and order the right amount. The board count is also shown, but the linear metre figure is what you will actually order from a supplier.

Related

• Drywall Ceiling Grid Calculator: Materials
• Drywall Estimate Calculator: How to Price a Job
• Drywall Contractor Bids Calculator: Estimate Job Cost

in length | Fence length | m | 10 | 0
in bw | Board width | mm | 150 | 0
in overlap | Overlap | mm | 25 | 0
out count | Boards needed | boards | ceil(length / ((bw - overlap) / 1000)) | 0
out gauge | Visible board spacing | mm | bw - overlap | 0
out total | Total board length | m | ceil(length / ((bw - overlap) / 1000)) * (bw / 1000) | 2