Calculating the correct number of deck boards prevents costly extra trips to the lumber yard and leftover material. Here is the practical method used by this calculator:
Measure the length and width of the area the boards will cover. For L-shaped or multi-level decks, calculate each rectangle separately and add the results.
Nominal sizes are not the finished size. A “2×6” or “5/4×6” deck board is typically 5.5 inches wide. Many composite boards are closer to 5.25 inches. Always check the product label.
Leave a gap between boards for drainage and expansion. Common gaps:
10% is a solid default for a simple rectangular deck. Increase to 15% for diagonal laying or complex shapes, and 15–20% for picture-frame borders or herringbone patterns.
Longer boards (16–20 ft / 4–5 m) usually mean fewer end joints and less waste on longer decks.
Imperial: A 12 ft × 16 ft deck (192 sq ft) using standard 5.5″ boards with a 1/8″ gap and 10% waste typically needs about 29–34 boards of 16 ft length.
Metric: A 3.7 m × 4.9 m deck using 14 cm boards with a 0.5 cm gap and 10% waste typically needs a similar number of 4 m or 5 m boards. Use the calculator above for exact numbers.
Yes. Always add at least 10% for cuts, defects, and future repairs. It is cheaper to have a few extra boards than to stop the job mid-way.
Yes. A 45° layout multiplies the linear footage by approximately 1.414 and usually needs a higher waste percentage because of the angled cuts.
A common rule is two screws per board at every joist. This calculator estimates fasteners based on your chosen joist spacing. Stainless or coated deck screws are recommended.
In-depth articles to use with the calculator:
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