Home Improvement
Decking Calculator
Enter deck length and width, board width, gap and waste to see linear metres and packs.
How much decking do I need?
Decking quantity is driven by deck area and how board width plus the expansion gap pack across the span. Count boards across the width, multiply by deck length for linear metres, then add waste for end cuts, picture-frame borders and awkward posts. Packs quote a total board length — divide your linear need by that pack length and round up. Composite boards often specify a minimum gap that differs from timber; use the manufacturer figure. Joists, posts and fixings are separate purchases. For even gap layout experiments see the board spacing calculator, and for general floor coverage maths the flooring calculator.
Worked example
A 4 × 3 m deck with 140 mm boards and 5 mm gaps needs ceil(3 / 0.145) ≈ 21 boards across. Linear ≈ 21 × 4 = 84 m; +10% ≈ 92.4 m. A 14.4 m pack → 7 packs.
Limits and assumptions
Assumes boards run the length direction. Diagonal decks and herringbone patterns need substantially more waste. Framing timber is not included.
Frequently asked questions
Board width — cover or actual?
Use the laid width including the tongue or the face width the gap sits against, consistent with how you measure the gap.
What waste percentage should I use?
Straight runs often use 5–10%. Complex shapes, many cut-outs or picture frames commonly need 15%+.
Are packs always whole boards?
Many packs mix lengths. Buy enough total linear metres; check the pack label for workable lengths.
Do I need hidden fixings in the calculation?
No — this estimates board metres only. Screws and clips are counted from the board supplier’s fixing charts.