Composite Decking Calculator
Composite deck boards and clips needed.
Enter your values
Enter the deck area in sq ft.
Enter the board width in in.
Enter the board length in ft.
Enter the joists crossed per board you are working with.
Enter the waste allowance in %.
Results update instantly as you type — no submit needed. Your values are remembered on this device, and the shareable link reopens the calculator with exactly these numbers.
- Boards needed
- 45
- Board coverage each
- 7.33 sq ft
- Hidden fastener clips
- 540
- Face screws (if used)
- 540
Quick answer
Composite decking needs boards to cover the deck area plus waste, plus one clip per joist crossing per board.
boards = ceil(deck area x (1+waste%) / board coverage)
At a glance
| What it does | Composite deck boards and clips needed. |
|---|---|
| Category | Home & DIY |
| Inputs needed | Deck area, Board width, Board length, Joists crossed per board, Waste allowance |
| Main output | Boards needed |
| Formula | boards = ceil(deck area x (1+waste%) / board coverage) |
| Cost | Free — no sign-up, no download |
How to use the Composite Decking Calculator
- 1Enter the deck area and the composite board dimensions.
- 2Enter how many joists each board typically crosses.
- 3Add 10% waste for end cuts and picture-frame borders.
Inputs explained
- Deck area(sq ft)
- Enter the deck area in sq ft.
- Board width(in)
- Enter the board width in in.
- Board length(ft)
- Enter the board length in ft.
- Joists crossed per board
- Enter the joists crossed per board you are working with.
- Waste allowance(%)
- Enter the waste allowance in %.
Worked example
Using the values the calculator loads with:
Inputs
- Deck area300 sq ft
- Board width5.5 in
- Board length16 ft
- Joists crossed per board6
- Waste allowance10 %
Results
- Boards needed45
- Board coverage each7.33 sq ft
- Hidden fastener clips540
- Face screws (if used)540
Frequently asked questions
Hidden clips or face screws?
Hidden fastener clips give a clean look; face screws are cheaper and easier for DIY.
Does this include the substructure?
No, use a separate joist and beam calculation — this only covers the decking boards and fasteners.
What do I need to enter into the Composite Decking Calculator?
Just 5 values: deck area, board width, board length, joists crossed per board, waste allowance. Every field starts with a realistic example, so you can change one number at a time and watch the result update instantly.
How does the Composite Decking Calculator work out the answer?
Composite decking needs boards to cover the deck area plus waste, plus one clip per joist crossing per board. It applies the formula boards = ceil(deck area x (1+waste%) / board coverage) and shows the working so you can check each step by hand.
Is the Composite Decking Calculator free, and do I need an account?
It is completely free with no sign-up, no download and no usage limit. Everything is calculated in your browser, so the numbers you type never leave your device.
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.