How to use the deck board calculator
- Enter the deck length in the direction boards run and its width across the rows.
- Use actual board width, the intended installation gap, and the available stock length.
- Choose an allowance for trimming and defects. Confirm the resulting layout against joists and the decking manufacturer’s guidance.
The formula
Rows = ceiling((deck width in inches + gap) ÷ (board width + gap)); boards = rows × ceiling(deck length ÷ stock length)
Worked example
A 16 × 12 ft deck using 16 ft boards, a 5.5 in face, and ⅛ in gaps needs 26 rows. With a 10% allowance, plan for 29 boards.
Before you measure and cut
The final row may need ripping to width. Equal gaps alone do not guarantee equal edge margins.
This estimates surface decking, not joists, posts, fasteners, or structural capacity. Longitudinal butt joints need suitable support.
Frequently asked questions
Does this optimize offcuts?
No. Each row is counted independently. Use the linear cut optimizer for a detailed length-cut plan.
Can I use it for diagonal decking?
The formula assumes boards parallel to a deck edge. A diagonal deck requires a layout-based takeoff.