Deck Square Footage Calculator
Enter your deck size and board width to get square footage, the lineal feet of decking and the number of boards to order — for straight or diagonal layouts.
Estimates only. Decking counts vary with picture-frame borders, breaker boards and stair treads. We measure your exact deck for a firm materials list.
Get a Free Decking QuoteHow to Use the Square Footage Calculator
Enter your deck's length and width in feet. Pick your decking board width — 5.5" boards (nominal 6") are the most common, and 3.5" boards (nominal 4") give a tighter, more detailed look. Choose a straight or diagonal layout, set your board length and trim-waste allowance, and the calculator returns your square footage, the lineal feet of decking, and how many boards to order.
Square Footage and Lineal Feet Explained
Square footage is simply length × width. Lineal feet is different — it is the total running length of deck boards needed to cover that area. To get it, we divide the deck area by the coverage of one board (its face width plus a 3/16" gap). A 5.5" board covers about 5.69" with the gap, so a 192 sq ft deck needs roughly 405 lineal feet before waste.
Then we add trim waste — 5% for a simple rectangle, 10% is typical, and a diagonal layout adds about 5% more because every board is cut at an angle. Order the waste; running short mid-project costs more than a few extra boards.
Decking Materials for San Diego
Board width and spacing are the same whether you build in wood or composite, but the material changes cost and upkeep. Low-maintenance composite decking and classic redwood both come in 5.5" and 3.5" widths. Once you know your lineal feet, run the numbers through our deck cost calculator to price the full build.
Frequently Asked Questions
How do I calculate deck square footage?
Multiply the deck length by the width in feet. A 16 ft by 12 ft deck is 192 square feet. For an L-shape, split it into rectangles and add them together.
How many deck boards do I need per square foot?
With 5.5-inch boards and a 3/16-inch gap, one square foot needs about 2.1 lineal feet of decking. Divide your total lineal feet by the board length to get the board count, then add 5 to 10 percent for waste.
Does a diagonal deck use more material?
Yes. A diagonal or 45-degree layout adds roughly 5 to 15 percent more decking because each board is cut at an angle, leaving off-cuts you cannot always reuse.
What gap should I leave between deck boards?
A 1/8 to 3/16 inch gap is standard so water drains and boards can move. Composite boards use hidden clips that set the gap automatically; this calculator assumes 3/16 inch.