Deck board calculator
Estimate deck boards, joists, and screws from deck size, board width, gap, joist spacing, and waste.
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Tool guide
Deck board calculator: how it works
Practical information to understand the result and use this tool correctly.
About Deck board calculator
This deck board calculator turns a rectangular outdoor deck into a materials list: decking boards, joists, rim length, and screw boxes. It is for a simple rectangle, not a multi-level deck with stairs, landings, or angled corners.
Boards run along the length or the width you choose. Rows are the across dimension divided by board width plus gap, rounded up. Each row is split into stock lengths, then the waste percent is applied and the total is rounded up. A 140 mm board with a 5 mm gap is a common composite or treated-pine pitch.
Joists sit perpendicular to the boards. The count is the run divided by center-to-center spacing, rounded up, plus one so both ends are included. Each joist is cut to the across dimension. Rim length is two times the run and does not include a ledger, beam, or posts.
Screws are rows times joists times screws per crossing, then packed into the box size you enter. Optional prices are a material check only. The tool does not size beams, footings, spans for snow load, or local code. Confirm joist spacing with the board manufacturer, often 400 mm for diagonal or composite and 600 mm for some timber decks.
How to use it
- 1Enter deck length and width in meters.
- 2Set board width, gap, and the stock length you can buy.
- 3Choose board direction and joist spacing, then add a waste percent.
- 4Optional: set screws per crossing, box size, and unit prices.
- 5Read boards, joists, rim meters, and screw boxes, then copy the list.
Frequently asked questions
- How are deck boards counted?
- Rows equal the across dimension divided by board width plus gap, rounded up. Pieces per row equal the run divided by stock length, rounded up. Waste is applied to that product and the result is rounded up again.
- What joist spacing should I use?
- 400 mm (about 16 in) is a common preset for composite and diagonal boards. 600 mm (about 24 in) is a wider timber preset. Always match the board warranty and local code; this tool only counts pieces.
- Does it include posts, beams, and stairs?
- No. It estimates decking, joists that span the across dimension, rim length along the run, and screws. Ledger, beams, posts, footings, and stairs are separate.
- Is the calculation private?
- Yes. Dimensions stay in the browser. Nothing is uploaded to calculate boards or prices.
- Can I enter inches?
- Inputs are metric. 5.5 in is about 140 mm, 16 in spacing is about 406 mm, and 12 ft is about 3.66 m. Use the patio presets as a starting point and adjust.