Quick estimate mode — for joists, posts, fixings, concrete and cost breakdown:
Full calculator →
Quick Deck Calculator
Enter your deck dimensions and board size to get the number of boards to buy.
Your Deck
Result
Boards to buy
–
boards
Always buy 10% extra for end cuts and future repairs.
Need joists, posts and fixings too?
Full calculator covers the complete deck frame, concrete footings and hardware.
How to calculate deck boards
The formula
Runs = deck width ÷ (board width + gap). Boards per run = ⌈deck length ÷ board length⌉. Total = runs × boards per run × 1.10 (waste).
Which board width should I choose?
95–120 mm suits most decks. Narrower boards are less prone to cupping but need more fixings. Wider boards lay faster but can warp more on exposed sites.
What gap should I leave?
A 5 mm gap is standard — it allows drainage and airflow while keeping the surface comfortable underfoot. Use 3 mm for composite boards that expand less. Timber boards swell when wet, so never butt them tight.
Pro tip: Orient boards so the length runs away from the house — it looks better and cuts are hidden at the outer edge where they matter less.