Deck Material Calculator

How many deck boards do I need?

Start with the rectangular deck dimensions, then choose the direction of the boards. The run is the distance each row travels. The covered width is the perpendicular distance across all rows.

Rows = round up ((covered width + side gap) ÷ (actual board width + side gap)). The gap is counted between rows, not outside the first and last boards. Edge boards may need ripping, and first/last row details must be checked on site.

Actual board width, gaps and cutting loss

Enter actual measured width, not a nominal board name. A common 1×6 decking profile can be about 5.5 inches wide, but products differ. Use the manufacturer’s dimensions and spacing requirements for your specific material and conditions.

A saw cut removes material. If a stock board is long enough for more than one full run, the calculator estimates how many repeated cuts fit, including the kerf:

Full-run cuts per stock board = round down ((stock length + kerf) ÷ (run + kerf)). It then rounds rows divided by those cuts up to a whole number of stock boards. End trimming and perimeter clearances are not modeled.

Example: a 12-by-10-foot deck

With boards along the 12-foot length, 5.5-inch actual width, a 1/8-inch side gap and 16-foot stock, the estimate is 22 rows. One full 12-foot run fits each stock board. The base is 22 stock boards; adding 10% and rounding up gives 25 boards to buy. The deck area is 120 square feet. Those stock dimensions and gaps are illustrative, not a product recommendation.

Short stock boards and joints

If stock boards are shorter than the run, the estimate uses rows multiplied by the rounded-up number of pieces per row. It does not reuse offcuts between jointed rows. This is a conservative purchasing allowance, not a joint layout or an optimized cut list.

Butt joints need suitable supports and product-specific end gaps. The calculator does not estimate face screws in this case. Check the project plan before purchasing or cutting.

Face screws and optional budget

For uninterrupted board runs, the optional face-screw estimate assumes support lines at no more than the spacing you enter, including both ends, and two screws per row at every support line. It applies the same extra percentage as a spare-screw allowance. The support count is only a geometric assumption, not an instruction for framing or structural spans.

Hidden clips, butt-joint connections, framing connectors and specialist fasteners are excluded. The optional budget multiplies the buy count by the price per stock board. It excludes framing, hardware, taxes, labor, delivery and other project costs.

Check the product instructions

Trex’s board-quantity guide discusses actual board width, while its board-spacing guide distinguishes face screws from hidden clips. Product requirements differ; use the installation instructions applicable to the boards and fastening system you buy.

This tool estimates straight decking surface materials for a rectangle. It excludes diagonal patterns, picture-frame borders, obstacles, stairs, railings, joist/beam/post sizing, footings, load capacity and building-code approval. All calculations run in your browser; no project submission is required.