Deck Board Calculator: How Many Boards, and Which Lengths to Buy
Enter your deck size and get a board buy list by length, a cut plan with staggered joints, the layout drawn to scale, joist and screw counts. Feet or metres. Runs in your browser.
When to use this
- You are pricing a new deck or a deck re-board and need to know how many boards to order.
- You can buy several board lengths and want the combination that wastes the least.
- You want to see where butt joints land on the joists before you cut anything.
How to use
- Choose feet or metres, then enter the deck length and width.
- Set the board width, the gap between boards and the joist spacing, or keep the defaults.
- Tick the board lengths your supplier sells. Add prices if you want a cost comparison.
- Press Calculate buy list, then check the layout, the cut list and the comparison table.
- Copy the buy list, download it as a CSV, or copy the link to save this exact plan.
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Report a problem or suggest an improvement
Nothing is sent until you press Send. Your measurements are included only if you tick the box, and you can see the full report below first.
Examples
- 12 x 16 ft deck, 5.5 in boards, 1/8 in gaps: 26 rows of one 16 ft board each, 13 joists at 16 in centers, 0 percent cutting waste. The last row needs a lengthwise rip.
- 20 x 30 ft deck: Boards are longer than the 20 ft maximum stock, so joints are placed on joists and staggered. The tool compares mixed lengths with buying one length only.
Understanding the result
Boards to buy is the cut plan plus spare boards. Cutting waste is the board length left over after every piece is cut, as a percent of the board length bought. The comparison table shows how much the choice of board lengths changes both waste and cost. Joists are counted across the board direction with one at each end.
Limitations
- This is a material estimate, not a structural design. Joist size, span, footings, ledger and railing rules depend on your local building code.
- Diagonal layouts estimate each strip from its longest edge. Offcut triangles are not re-used, and joint positions are not planned.
- Board widths, gaps and expansion rules vary by product. Use your board maker's instructions.
- Stairs, picture-frame borders, cantilevers and curved edges are not modelled.
FAQ
How many deck boards do I need?
Divide the deck width by the board width plus the gap and round up to get the rows. Each row is as long as the deck. The tool then breaks each row into purchasable board lengths so you can see how many boards that is.
Which board length wastes the least?
The one that divides your deck length with little left over. A 16 ft deck uses 16 ft boards with no waste. The tool tries every length you tick and a mixed purchase, then shows the waste for each.
How far apart should butt joints be?
Joints should land on a joist and be staggered so neighbouring rows do not join on the same joist. The layout drawing shows each joint so you can check it.
Why does the last row need ripping?
Rows are whole boards plus gaps. If the deck width is not an exact multiple, the last board is cut narrower. You can also adjust the first and last rows equally for a balanced look.
How many screws do I need?
Face screws are counted as two per board at every joist it crosses. Hidden clips are counted as one per crossing. A spare margin is added.
Is my information stored?
No. All calculations run in your browser. The share link stores your measurements after the # sign, which browsers do not send to any server.
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