Measure the deck
Multiply length by width for the deck platform. Split irregular shapes into rectangles and add them together.
Tool Switcher: Deck
Project toolsTools
Deck planning tool
Deck Calculator
Turn a deck footprint into whole boards, joists, posts, concrete, and fasteners for a simple rectangular deck.
- Boards, joists & posts
- US and metric units
- Full material ticket
Deck planning tool
Deck Calculator
Estimate deck boards, joists, posts, concrete, and fasteners.
Methodology
From footprint to a material ticket
Count the boards
Each board row spans the deck length. Divide the width by the board width plus gap, then add the waste allowance.
Frame joists and posts
Joists run on center across the deck length, and posts support the beams along the perimeter. Both use standard spacing.
Plan concrete and fasteners
Concrete scales with the post count and fasteners with the board and joist crossings. Both are planning estimates.
Worked example
A 16 × 12 ft deck
192 ft²deck platform
÷5.625 inboard width + gap
=29 boards13 joists
A 16 × 12 ft deck in 5/4×6 boards needs about 29 boards, 13 joists, 10 posts, 20 bags of concrete, and 754 screws before a 10% allowance.
Frequently asked questions
A second look at the estimate.
How many deck boards do I need?
Divide the deck width by the board width plus gap to get the number of rows, then add waste. A 16 × 12 ft deck in 5/4×6 boards takes about 29 boards.
What joist spacing should I use?
Sixteen inches on center is standard for most residential decks. Diagonal or composite decking often needs 12 inches on center.
How many posts and footings do I need?
Posts are spaced along the beams, typically every 6 to 8 feet. Each post gets one concrete footing. This calculator uses an editable post spacing.
Can I enter metric dimensions?
Yes. Metric mode uses metres for the deck and post spacing, and centimetres for board width and gap.
How is the cost estimated?
Enter a price per board and the calculator multiplies it by the whole-board count. Without a price, no cost is shown.
Sources and limitations
This tool estimates deck materials for planning. It is a material estimate only — it does not provide structural or engineering conclusions, and it does not assess spans, loads, connections, footing depth, or local building code requirements, or retrieve live prices.
- American Wood Council — DCA 6 Prescriptive Residential Wood Deck Construction Guide — reference for joist and post spacing and footing guidance.
- Board foot calculator — estimate framing lumber by volume.
- Concrete bag calculator — compare bag sizes for the footings.
Board, joist, post, concrete, and fastener counts are planning estimates for a simple rectangular deck. This tool estimates materials only and does not provide structural or engineering conclusions. Verify spans, loads, connections, and footing depth against DCA 6 and local code before building.
Last reviewed: September 7, 2026