Deck material calculator
Estimate how many boards, joists, beams and posts a deck project needs.
Deck material calculator
Estimate how many boards, joists, beams and posts a deck project needs.
Enter your deck dimensions to see the material estimate.
Boards needed
Project summary
How it works
These are material estimates, not structural engineering specifications. Check local building codes for structural requirements.
Deck material calculator
Why board count matters more than area
A deck is not just square footage. The number of boards you need depends on the board width, the gap between boards, and the waste from cuts and angled edges. Two decks of identical square footage can need substantially different quantities of lumber depending on how the boards are laid out and how much waste the shape creates.
Framing is the hidden cost
The decking boards are what you see, but the joists, beams and posts underneath are what hold everything up. Joist spacing determines how many framing members you need, and beam and post spacing determine how many of each. These numbers add up faster than most people expect, and they are the part of the material list that is hardest to add to later once the deck is built.
The waste allowance covers real losses
Cutting boards to length wastes material at every cut. Angled edges, curved sections and boards that do not quite reach the end of a run all contribute. Ten percent is a reasonable allowance for a straightforward rectangular deck. An irregular shape or a deck with many angles may need more.
Frequently asked questions
How many deck boards do I need for a 12 by 16 foot deck?
Using standard 5.5 inch wide boards at 12 feet long with a 3/16 inch gap and 10 percent waste, a 12 by 16 foot deck (192 square feet) needs about 50 boards. The exact number depends on the board dimensions you choose and the waste allowance. Enter your own dimensions above for the precise count.
How far apart should joists be on a deck?
Most residential decks use joist spacing of 16 inches on centre, which is the default on this calculator. Heavier loads or thinner decking may call for 12 inch spacing. Check your local building codes, which may specify maximum joist spacing for the decking material and thickness you are using.
How much does it cost to build a 12 by 16 foot deck?
Costs vary by region and material, but a pressure treated pine deck of that size typically runs between 4000 and 8000 dollars for materials alone. Cedar or composite decking raises the price significantly, often double or triple. Labour, permits and hardware add to the total. The calculator gives you a material list so you can get accurate quotes from suppliers in your area.
What is the cheapest way to build a deck?
Pressure treated pine is the most affordable decking material in most markets. Keeping the design simple and rectangular reduces waste and labour. Building at ground level or on a concrete pier foundation is cheaper than a raised deck with a staircase. Buying materials in bulk from a lumber yard rather than a retail store also saves money. The calculator helps you avoid over-ordering, which is a common source of wasted material.
How long does it take to build a deck?
A straightforward ground level deck of moderate size takes an experienced builder two to four days. Larger or multi-level decks with stairs and railings can take a week or more. Permits, inspections and weather delays add time. The calculator focuses on material quantities, but having a complete material list before you start helps avoid mid-project trips to the supplier, which slow progress.
Do I need a permit to build a deck?
Most jurisdictions require a building permit for any deck attached to a house or elevated more than 30 inches above grade. Freestanding ground level decks may or may not need a permit depending on local code. Check with your local building department before starting. The calculator produces a material list you can include with your permit application.
Can I build a deck on sloped ground?
Yes, but the framing gets more complex. You will need posts of varying lengths to create a level surface, and the beam and footing layout must account for the slope. A simple gravity-based design with concrete piers works well for moderate slopes. The calculator gives you a baseline material estimate for a flat deck, and you can adjust post quantities manually for the slope.
What is the lifespan of a pressure treated deck?
Pressure treated lumber typically lasts 15 to 20 years with proper maintenance. Regular cleaning and re-staining or re-sealing every two to three years extends the life. Cedar lasts 20 to 25 years. Composite decking can last 25 to 50 years depending on the brand. The calculator helps you estimate material costs so you can compare the upfront price against expected lifespan.