Deck Calculator – Boards, Joists & Screws

A deck takeoff multiplies three lists. Decking: area ÷ (board width + gap) gives lineal meters, then pieces by length - a 14 cm board with a 5 mm gap covers 14.5 cm of width per course. Structure: joists at 40 cm (16 in) centers - 2×8 spans up to 3.6 m, 2×10 to 4.6 m - plus beams, posts and footings. Fasteners: 2 screws per joist crossing, roughly 350 screws per 100 ft² (9.3 m²). Worked example: a 4 × 3 m deck needs 28 boards of 3 m, 9 joists, 6 post footings and about 500 stainless screws. Use ground-contact treated lumber or composite within 30 cm of grade, and check the permit line: decks over 18 m² or above 75 cm usually need drawings.

1. 1

   Measure the space

   Record the deck dimensions, board width and joist span at the widest and longest points.

2. 2

   Enter the values

   Type the measurements into the calculator and select your units.

3. 3

   Apply the formula

   The tool computes Boards = Deck Area ÷ (Board Width × Length); Joists = Width ÷ 0.4 + 1; Screws = Boards × Joists × 2 for your inputs instantly.

4. 4

   Add waste and order

   Review the total with a 5-10% margin and round up to whole units.

• Using nominal as actual sizes

• Spacing joists too wide

• No ground-contact treatment