Building a deck
Pages in this list checked · How we check
Building a deck takes 7 of the pages on this site, not one. From the board count to the concrete under it. Work down the list in order: the area sets the board count, the board count sets the cost, and the footings are the part people forget until the posts are already cut. Each page in the list computes its own figure from a published formula and prints the working, so the whole sequence can be checked rather than trusted.
- 1Deck Board CalculatorBoards for the surface, including the gap between themCalculator
- 2Board Foot CalculatorWhat the lumber yard is actually charging you forCalculator
- 3Concrete CalculatorFootings for the posts, in bags or cubic yardsCalculator
- 4Stair CalculatorRise and run once you know the height off the groundCalculator
- 5Square Footage CalculatorThe deck area, for anything sold by the square footCalculator
- 6What a Deck Costs to BuildWhat the whole job runs, with the rangesGuide
- 7How to Measure a Room for FlooringMeasuring an irregular space without guessingGuide
What goes wrong on this job
The footings are the part that gets forgotten
Boards and joists are visible and get counted. The concrete under the posts is not, and it is ordered last, usually after the posts are already cut. A 16 by 12 deck on six 12-inch Sonotubes set 4 ft deep takes about 0.8 cubic yards — under a full yard, which is the awkward quantity where bags beat a truck.
Board count is not deck area divided by board area
The gap between boards is real material you do not buy. A 5/4x6 laid with a 1/8 in gap covers 5.625 in of width per board rather than 5.5, and across a 12 ft run that difference is two boards. Count by coverage width, not by nominal size.
Waste on a diagonal is not the same as on a square
A rectangular deck runs about 5% waste. Lay the boards at 45 degrees and it goes to 15%, because every board meets the frame at an angle and both ends become offcuts.
A 16 × 12 deck, typical quantities
| Item | Quantity |
|---|---|
| Surface area | 192 sq ft |
| 5/4×6 boards at 12 ft | ≈ 41 |
| Concrete for six 12 in footings, 4 ft deep | ≈ 0.8 cu yd |
| Waste allowance, square lay | 5% |
| Waste allowance, 45° lay | 15% |
Typical figures for orientation. Every one is recomputed by the calculators above from the dimensions you actually have.
What the figures rest on
Every quantity above is computed by one of the calculators in the list, from these published standards.
- American Wood Council DCA 6 — prescriptive residential deck construction
- International Residential Code R507 — decks
- NIST Office of Weights and Measures — methods of sale for lumber
- American Lumber Standard Committee — nominal vs actual dimensions
- American Concrete Institute
- Portland Cement Association
- ANSI Z765 residential square footage measurement standard