Deck planning · Guide 7 of 10 · 4 min readUpdated
How to calculate deck boards
Choose board direction and stock lengths by joints, handling and useful offcuts, then calculate an order that matches the deck you intend to build.
Compare the work created by each board direction
A board direction that reaches across the deck in one piece can reduce end joints and keep the field visually continuous. It can also demand longer, harder-to-handle stock. Turning the field may make standard lengths more useful, but introduces a different joist direction or more supported joints.
The smallest leftover pile is not always the best cutting plan. A plan that relies on many small pieces can add layout, backing and fastening work. Compare complete courses and joint locations, then decide whether the material saving is worth the extra work and appearance.
Example: a 12-foot-wide field
A nominal 12-foot stock board is not automatically enough for every 12-foot finished dimension. Borders, gaps and required end trimming alter the usable length. Compare the actual field piece with the supplier’s usable stock, then decide whether a longer board or a deliberately supported joint is the practical purchase.
Measure the finished footprint and choose the board direction
Enter the finished outside dimensions of the decking, including any picture frame. For an L-shape, measure the rectangular corner cutout. Draw angled or more complex outlines in the Deck Designer, then open Numbered cuts & stock comparisons to carry the footprint into this board calculator.
The board run follows the length of a course; the dimension across the boards controls the course count. Changing board direction can change stock use and joints. The planner keeps the entered joist direction fixed, so rotating the decking may require a different support detail.
- Use actual board face widths, not nominal lumber sizes.
- Choose the border rows and perimeter edges before laying out the field.
- Enable only stock lengths you can obtain and handle on site.
- Allow for fascia, stairs and breaker boards separately.
Calculate straight courses within the field
The field is the area inside any selected picture-frame boards and their gaps. The planner calculates courses across that field and clips each course to the footprint. On an L-shape, some courses are shorter and one may need a notch at the inside corner.
Course count = round up [(field width + gap) ÷ (actual board width + gap)] Last course width = field width − [(courses − 1) × (board width + gap)]
This formula describes straight, parallel courses across a rectangular field. The calculator balances narrow outside rips where applicable. Angled and herringbone layouts use their actual clipped piece geometry; check perimeter cuts and minimum usable widths separately.
Follow the numbered cuts into the purchase list
F001 and the other F marks are field pieces; B marks identify border pieces. Select a board in the drawing or find it in the numbered cut list. Each cut is assigned to a stock board such as FS01 or BS01 in the stock cutting sheet.
A rectangular field with uninterrupted courses has lineal footage equal to course count multiplied by the run. For an L-shape or a jointed layout, sum the actual blank lengths. Long-point mitre blanks and notched pieces consume more material than their finished visible area alone suggests.
Cut-plan lineal footage = sum of individual blank lengths Order = allocated stock boards + whole-board spares
- Field and border stock are kept separate because profiles or colours can differ.
- Offcuts are reused within the same profile when they fit the listed cuts.
- The planner includes blade kerf; it does not reuse ripped strips or mitre triangles.
Compare practical stock combinations
Compare mixed lengths, the price-led mixed plan, and each enabled stock length on its own. Fewer boards does not always mean lower cost. Check the total price, joint count, spare boards and remaining offcuts together.
The mixed plans use practical stock packing, not an exhaustive search. For straight courses, supported splice locations and attempts to stagger adjacent joints influence the cuts. Angled and herringbone pieces need their pattern backing reviewed in the Deck Designer; shorter stock may create more pieces and joints.
Enter positive prices for all enabled lengths and both profiles when using borders. Costs cover the listed decking order and spares; taxes, delivery, framing and hardware are separate.
Check the saw allowance and the support
Two exact 6-foot cuts need more than 12 feet of stock when the blade removes material. With a 1/8-inch kerf, they need at least 144 1/8 inches between sound square ends. Factory end trimming is another allowance; measure the usable stock length.
Straight field joints on perpendicular joists are placed on the entered grid where possible. Angled and herringbone joints need backing laid out in the Deck Designer. Confirm actual bearing, board-end support, border backing and the selected fastening detail before treating any cut plan as ready to build.
n equal cuts need n × cut length + (n − 1) × kerf
Technical references
Confirm the current product literature and requirements for the material and assembly being installed.