How many decking boards (lineal metres) do I need?
Published · Updated · By Sai Nath
Divide the deck width by the board width plus the gap, and round up: that is the boards across. Multiply by the deck length to get lineal metres, then add 10% to order. A 6 m × 4 m deck with 90 mm boards and 5 mm gaps needs 43 boards across and 258 m, so order 283.8 m.
Sizes on this page are metric. The formula works the same in feet if you keep every measurement in one unit. Checked on 28 October 2026: every figure below was worked by hand and matches the formula in MeisterCalc's Decking calculator.
How do I work out how many boards I need for a deck?
Three steps. Boards run along the deck length. The width is the other way, across the boards.
- Boards across = deck width ÷ (board width + gap), rounded up to a whole board.
- Lineal metres = boards across × deck length.
- To order = lineal metres × 1.10, so there is 10% for cuts and offcuts.
Lineal metres, square metres and a count of boards are three different things. The square metres are the deck's area (length × width). Lineal metres are the total run of board laid end to end. A board count depends on how long the boards are, which is the last step further down.
Worked example: a 6 m × 4 m deck
Deck length 6000 mm, deck width 4000 mm, boards 90 mm wide, 5 mm gap.
- Area: 6 × 4 = 24 m².
- Board plus gap: 90 + 5 = 95 mm.
- Boards across: 4000 ÷ 95 = 42.1, which rounds up to 43.
- Lineal metres: 43 × 6 = 258 m.
- To order: 258 × 1.10 = 283.8 m.
One honest note on the rounding. Forty-two boards and their 41 gaps cover 42 × 90 + 41 × 5 = 3985 mm. That leaves 15 mm, and after one more gap only about 10 mm of face for the 43rd board. Rounding up counts that sliver as a whole board, which is safe for ordering. On site you would rather nudge the gap a little or rip the last board to suit, so check the layout before you cut anything.
How many lineal metres of decking per square metre?
Lineal metres per square metre = 1000 ÷ (board width + gap in mm). It is the metres of board in one square metre of deck before any waste. For the 90 mm row: 1000 ÷ (90 + 5) = 10.53 m, and 10.53 × 1.10 = 11.58 m with 10% extra.
| Board face + 5 mm gap | Lineal metres per m² | With 10% extra |
|---|---|---|
| 90 mm | 10.53 m | 11.58 m |
| 140 mm | 6.90 m | 7.59 m |
| 190 mm | 5.13 m | 5.64 m |
The per-square-metre figure is an average. A real deck rounds up row by row, so use it for a first estimate and the full calculation for the order. Our guide to square metres to lineal metres of decking goes through the conversion in more detail.
How many decking boards for 15 m², 40 m² or 3 m × 3 m?
For an estimate, multiply the area by the lineal metres per square metre. 15 m² of 90 mm board at a 5 mm gap is about 15 × 10.53 = 158 m before waste. For an order, do the sum with the real width and length, because the rounding changes the answer. A 5 m × 3 m deck (15 m²) with the same boards is 3000 ÷ 95 = 31.6, so 32 boards across, 32 × 5 = 160 m, and 176 m with 10% extra.
The same 6 m long × 4 m wide deck in three board sizes, 5 mm gap:
| Board face | Boards across | Lineal metres | Order (+10%) |
|---|---|---|---|
| 90 mm | 43 (4000 ÷ 95 = 42.1) | 258 m | 283.8 m |
| 140 mm | 28 (4000 ÷ 145 = 27.6) | 168 m | 184.8 m |
| 190 mm | 21 (4000 ÷ 195 = 20.5) | 126 m | 138.6 m |
For a 40 m² deck or a 3 m × 3 m deck, put your own length and width through the same three steps. You do not need a separate page for each size.
Does the gap between boards change the count?
Yes. Each board uses up its own width plus one gap, so the gap adds to the divisor. In the example above, ignoring the gap gives 4000 ÷ 90 = 44.4, or 45 boards. Using 95 mm gives 43. The gap is small, but it saves about two rows on a 4 m width.
The right gap depends on the board species and how dry it is when laid, so take the figure from the board supplier's installation guide, not from a rule of thumb. Our post on the gap between decking boards covers where to find it. Whatever you pick, enter it as the spacing in the calculation.
How much extra decking should I order?
Add 10% as a starting point. The extra covers end cuts, bowed or damaged boards and offcuts too short to use. A deck with many angled cuts or cut-outs for posts and fixtures wastes more, and MeisterCalc's help text for the Decking calculator suggests considering 15% for those.
How do I turn lineal metres into a number of boards?
Divide the lineal metres by the length of the boards you will buy, and round up. This is the step the calculator leaves to you, because it does not know what lengths your supplier stocks. Two cases:
- Boards as long as the deck. Each row is one board, so the count is the boards across: 43 in the example, plus whatever spare you add.
- Shorter boards, joined in a row. Each row needs the deck length covered by whole boards. Work out boards per row, round up, and multiply by the rows. With 3.6 m boards on the 6 m deck: 6 ÷ 3.6 = 1.67, so 2 boards per row, and 2 × 43 = 86 boards if every row is cut from new boards. If offcuts start the next row, the least you could buy is 283.8 ÷ 3.6 = 78.8, so 79 boards. Offcuts from one row can sometimes start the next, and where joins go is set by the frame and the board maker's instructions, so ask your supplier.
Board widths and stock lengths vary by supplier and by country, so confirm both before you order. In the Decking calculator, the width is the dressed (finished) face width, not the sawn or nominal size.
How do I use the Decking calculator in MeisterCalc?
- Open MeisterCalc and tap Decking on the home screen.
- Enter Deck Length (the way the boards run) and Deck Width.
- Enter Board Width (the face of one board) and Board Spacing (the gap).
- Read the results: Total Area, Boards Across, Lineal Metres and Order (+10%). The diagram of the deck updates as you type.
- To price it, enter a price per lineal metre. You get a total cost and a cost with a wastage percentage you can change. At 10.00 per metre, the example is 258 × 10.00 = 2580.00, and 258 × 1.10 × 10.00 = 2838.00 with 10% wastage.
- Tap the share icon to send the numbers as text or a PDF.
The calculator needs the board width to be less than the deck width and the spacing to be zero or more. Everything is in millimetres by default; Settings ▸ Units ▸ Default units ▸ Imperial (ft/in) switches to feet and inches.
What the Decking calculator doesn't do
- It does not work out stock lengths, joins or how many boards to buy. It gives lineal metres.
- It lays one run of boards per row. Diagonal layouts and picture-frame borders are not covered, so add those boards separately.
- It does not lay out joists or hidden fixings.
- It rounds up to whole boards, so it can count a thin last row as a full board, as in the example.
- Rules for the frame, joist spacing and fixings come from the board maker, the National Construction Code or your local standards, and the council. The app does not make a deck compliant.
Before you order
Measure the finished frame, not the plan. If the frame is out of square, the last row will taper, so check it first: how to square a deck frame takes a few minutes with a tape, and the diagonal check works on any rectangle. Then confirm board sizes, gap and lengths with your supplier, and order the extra.
Try it
Decking is not one of the three free calculators. Concrete, Stairs and Check Square are free; the other 12, Decking included, unlock with a weekly subscription that starts with a 3-day free trial, or with a one-time lifetime unlock, and Google Play shows the prices in your currency. It works offline on Android 7.0 or later. There's no iPhone version yet; you can join the iOS waitlist. For a comparison of apps, see the decking calculator app guide.