Woodworking calculator
Decking Board Calculator
Covering a deck takes more boards than a quick guess suggests, because each board has a width and you leave a small gap between rows for drainage and movement. This calculator takes your deck width and length, your board width, board length, and the gap you want, then returns the number of rows, the total board count, and the linear footage to buy. Enter your dimensions to plan a deck purchase with a sensible allowance built in.
How it works
The number of rows running across the deck depends on the board width plus the gap between boards. Each row effectively occupies its own width plus one gap, so the tool divides the deck width by that combined figure and rounds up to find how many rows it takes to span the deck. A wider gap means fewer boards but a more open surface; a tighter gap uses more boards.
Within each row, the deck length is covered by one or more boards laid end to end. The calculator divides the deck length by the board length and rounds up, then multiplies by the number of rows to get the total board count. Rounding up at each stage means you are never short, and any leftover becomes the offcut you trim at the ends of rows.
From the board count the tool also reports total linear feet, which is how decking is often priced and sold. It is wise to add a waste allowance of around 10 percent on top, more for diagonal or herringbone patterns, to cover trimming, mistakes, and the odd defective board. The result gives you a confident shopping list rather than repeated trips to the lumberyard.
Worked example
A 16 x 12 ft deck with 5.5 in boards (1/8 in gap), 16 ft long: 26 rows = 26 boards, roughly 416 linear feet of decking.
Frequently asked questions
Why include a gap between deck boards?
Gaps let water drain and air circulate, and they give the boards room to swell and shrink with the weather. A gap of about an eighth to a quarter inch is common and is built into the row spacing here.
How does board width change the count?
Each row covers its own width plus one gap, so narrower boards mean more rows and more total boards for the same deck, while wider boards cover the area with fewer rows but show fewer seam lines overall.
Should I add extra for waste?
Yes. Add roughly 10 percent on top of the calculated count for trimming, miscuts, and defective boards. Diagonal or herringbone layouts waste more at the angled ends, so allow 15 percent or more for those.
What is linear footage and why is it given?
Linear footage is the total length of all boards laid end to end, ignoring width. Decking is often priced and sold by the linear foot, so this figure converts your board count directly into a purchase quantity.
Does this handle diagonal decking?
The core count assumes boards run straight across the deck. Diagonal patterns need longer boards and waste more at the angled ends, so use this as a baseline and add a larger waste allowance for angled layouts.
Related calculators
Sources
These calculators are for planning and estimation. Engineering results (shelf sag, wood movement) use published average material properties; real boards vary by grade, grain, moisture and defects. Verify load-bearing designs with a professional.