Planning a new deck? Our free Deck Calculator works out how many deck boards, joists and screws your project needs from the deck size and board layout — so you can budget accurately and avoid extra trips to the timber merchant.
Boards are assumed to run along the deck length. Estimates include no wastage allowance — add around 10% for cuts and offcuts. Everything runs in your browser; nothing is uploaded.
How to Use
- Enter your deck’s length and width in feet.
- Add your board width and the gap you plan to leave between boards, in inches.
- Enter your joist spacing in inches (16 is standard for residential decks).
- Click Calculate to see the boards, joists and screws needed.
- Add around 10% extra to your order for cuts, offcuts and the odd mistake.
Key Features
- Board count based on your exact board width and gap.
- Joist count from your chosen joist spacing.
- Approximate screw count (two per board per joist).
- Total deck area for staining and sealing estimates.
- 100% private — all calculations happen in your browser.
FAQs
How many deck boards do I need?
Divide your deck width (in inches) by the board width plus the gap, then round up. The calculator above does this for you — a 10 ft wide deck with 5.5 in boards and a 0.25 in gap needs 21 boards.
What joist spacing should I use?
16 inches centre-to-centre is the standard for residential timber decks. Use 12 inches for diagonal decking patterns or heavier composite boards — check the board manufacturer’s guidance.
How many screws per deck board?
Two screws at every joist crossing is the rule of thumb, which is what this calculator estimates. Hidden fastener systems use clips instead — allow roughly the same count in clips.
Should I add extra for wastage?
Yes. Order around 10% more boards than calculated to cover cutting waste, defects and future repairs. It is far cheaper than a second delivery.
Is my project data sent anywhere?
No. The calculator runs entirely in your browser with JavaScript, so your measurements never leave your device.
Related Tools
You may also like our Flooring Calculator, Fence Calculator and Area Calculator.