Full-length board rows
A 16 × 12 ft deck using 5.5 in boards with a 3/16 in side gap needs 26 rows along its 16 ft length. With 16 ft stock, each row uses one board; 10% spare allowance gives 29 boards.
Compare board directions with an independent-row stock count.
Project measurements
Enter the gap required by your chosen product and conditions.
Use one currency throughout; tax, labor and delivery excluded.
Prices use your chosen currency consistently. Blank price skips cost. Example coverage, density, yield and prices are editable scenarios, not current product offers.
Material takeoff
Estimated purchase quantity
29 stock boards
26 board rows · lengthwise runs
Illustration is schematic, not an installation drawing.
| Deck surface | 192 ft² |
|---|---|
| Board rows | 26 |
| Stock pieces per row | 1 |
| Base stock board count | 26 |
| Added spare boards | 3 |
| Stock length purchased | 464 ft |
| Material cost | Not entered |
Method: Rows = ceiling[(across-deck width + gap) ÷ (actual board width + gap)]. Pieces per row = ceiling(run ÷ stock length). Round rows × pieces × allowance to whole boards.
Conservative independent-row count: offcuts are not reused between rows. Straight boards only; no picture frame, stairs, fascia, diagonal layout or end-gap adjustment. Board joints and supports must follow the product’s separate installation requirements. This is not a framing design.
Quantity and material-only cost estimate. Verify field measurements, product instructions and your purchase units. Labor, delivery, taxes, equipment and structural adequacy are excluded.
Calculations run in your browser. This tool does not request a location, retrieve live prices or send your measurements to a material supplier.
How to use the Decking Calculator
- 01
Enter deck length and width and choose whether boards run along length or width.
- 02
Enter actual board width, the side gap required by the product, and the stock board length you will buy.
- 03
Review rows and pieces per row, set a spare allowance and optional price per board, then save the estimate.
Examples
Changing direction
Run those boards across the 12 ft width instead: 34 rows each require one 16 ft stock board. With 10% extra, this method gives 38 boards. It intentionally does not reuse the 4 ft offcuts between rows.
Row coverage includes gaps
A row count is the ceiling of (across-deck width + side gap) ÷ (board width + side gap). Adding one gap to both numerator and denominator accounts for having gaps between boards, not beyond both outer edges. A final board may need ripping to width.
Stock planning is conservative
Every row rounds its own run length up to whole stock boards. No offcuts are shared between rows, so an optimized cut plan may use less stock. Trex publishes product-specific installation and gapping instructions; enter the values for your selected decking. Joist spacing, end joints, fasteners and supports require a separate approved layout.
What to know
- Material quantities and user-price scenarios only; no structural adequacy, code compliance or installation approval.
- Example product values are illustrative. Verify your measurements and current product label before ordering.
Common questions
Can the calculator design deck framing?
No. It counts surface boards only and does not determine spans, joist sizes, attachment, footings, loads or code compliance.
Does it handle diagonal boards or a picture frame?
No. Only straight parallel runs on a rectangle are modeled. Borders, stairs, fascia and angled layouts need separate quantities.
Does the gap mean a recommended gap?
No. It is an editable measurement input. Product, temperature and installation conditions determine suitable gaps.