Decking
Courses come from the board face plus gap. The total lineal footage follows the selected board direction or diagonal area model, then rounds up after waste to full stock boards.
Start with a ready-made 16 × 12 ft deck or enter your own dimensions. The material list, cost breakdown and visual model update together, so you can compare options and catch obvious planning mistakes before asking a supplier or builder for a final takeoff.
Start from a common footprint
Popular deck sizes
Each button updates the same calculator — no duplicate pages and no retyping.
How to use this deck calculator
- Enter the deck size. Type the length, width and height, swap the board run, or start from a common rectangular preset.
- Choose the visible finish. Pick a decking material and board direction. Open advanced settings only when you need stock length, framing, railing, stairs or pricing controls.
- Check the result from three angles. Review the 3D model, top-down plan and framing view beside the live quantities, cost categories, warnings and stated assumptions.
- Use your real prices. Edit unit prices from a local quote, then print, download CSV, copy the list or share the exact configuration.
What you can estimate
- Build a lumber-yard-ready list. Get board, joist, beam, post, footing, concrete, hanger, fastener, railing and stair quantities in one editable table.
- Choose the lower-waste board run. Switch boards between the length and width, compare stock lengths, or use a diagonal layout with an automatic or custom waste allowance.
- Compare decking materials on the same deck. Move between pressure-treated wood, cedar, redwood, composite, PVC and hardwood without re-entering your dimensions.
- Replace national seed prices with local quotes. Edit any unit price and add a labor allowance. Every subtotal and cost-per-square-foot figure recalculates immediately.
- Check what the calculator assumed. The result states its board gap, waste, joist spacing, support layout and footing limits instead of hiding those decisions behind one total.
Transparent by design
What the estimate is doing
Method reviewed 2026-07-23. Assumptions for your current deck are shown directly above the material list.
Framing
Joists run perpendicular to the boards. The model adds intermediate support beyond a 12 ft planning span and spaces posts no more than about 6 ft along each beam.
Hardware and features
Fasteners follow board-to-joist crossings. Railing uses open perimeter after the assumed house edge and stair opening; stair treads and stringers follow deck height and stair width.
Cost
Every line is quantity × editable unit price. The installed range is a broad comparison band, not a quote; local labor, permits, demolition, delivery, tax and site conditions can change the project total substantially.
Planning limit: this rectangular model does not calculate structural capacity, soil or frost conditions, ledger attachment, lateral loads, permits, taxes, delivery, demolition or irregular shapes. Treat the result as a first takeoff to verify, not an engineered design.
Deck calculator questions
How does the calculator estimate deck boards?
It divides the deck coverage direction by the board face plus gap to estimate courses, converts those courses into lineal feet, applies the selected waste allowance, then rounds up to full boards of your chosen stock length. Diagonal layouts use the deck area and effective course width because each board crosses the rectangle at a changing length.
Should deck boards run along the length or width?
Either may work, but the choice changes board cuts, seams, joist direction, beam direction and the assumed house edge in this rectangular planning model. Compare both orientations and then confirm the layout against the actual house connection, drainage, available stock lengths and framing plan.
What waste allowance should I use?
The automatic setting uses 10% for straight boards and 15% for a 45-degree layout. Simple rectangular decks with favorable stock lengths may need less; picture frames, poor stock optimization, defects, color matching or complex cuts may need more. Use the custom 5%–25% choices when you know your project.
What joist spacing should I use?
It depends on board material, product line, board thickness, installation angle, joist species and local requirements. Auto uses a conservative planning value for the selected material and diagonal layouts, but the final spacing must come from the decking manufacturer’s current span table and the structural design.
Does this replace a deck plan or permit review?
No. It is an early material and cost planner. It does not calculate soil bearing, footing diameter or frost depth, lateral loads, ledger fasteners, beam and joist species/grade capacity, bracing, snow loads, uplift, connectors or jurisdiction-specific details. Verify the final structure with the manufacturer, supplier, local authority and a qualified professional when required.
Is the deck calculator free and private?
Yes. There is no account or paywall. Calculations, saved inputs and exports run in your browser, and this site does not include analytics or advertising trackers. A share link stores the configuration in the URL so anyone with that link can reopen it.