Calculate-Compare-Decide
A complete bill of materials for your deck — boards, joists, beams, posts, footings, concrete, fasteners, stairs and railing — with a live blueprint, a board-waste optimizer, and a wood-vs-composite lifetime cost comparison.
Everything you need to buy, with waste included. Take this to the lumberyard.
Composite costs more upfront but barely needs maintenance. Wood needs staining every few years. Here's how they actually compare.
A deck material calculator estimates the number of deck boards, joists, beams, posts, concrete footings, fasteners, stairs and railing parts needed for a deck, based on its dimensions and chosen materials. It produces a full bill of materials with quantities, a waste allowance and an estimated total project cost.
Divide the deck width in inches by the board width plus gap. A 12 ft wide deck with 5.5″ boards and a ¼″ gap needs 144 ÷ 5.75 = 26 rows. Multiply by the deck length (16 ft) for 416 linear feet, then divide by the board length you buy.
Worked example — a 12 × 16 ft deck. Area = 192 ft². With 5.5″ boards and a ¼″ gap, each row covers 5.75″, so across the 12 ft (144″) width you need 26 rows. Each row runs the 16 ft length → 416 linear feet of decking. Joists at 16″ o.c. along the 16 ft length: 192 ÷ 16 + 1 = 13 joists, each 12 ft long. Two beams, three posts each = 6 footings, needing about 0.52 yd³ of concrete. Fasteners: 26 × 13 × 2 = 676 screws.
The board-length trap. Buy 16 ft boards for that deck and you need 26 — one per row, no cuts. Buy 12 ft boards and the naive approach is two per row = 52 boards, with a 4 ft offcut wasted from every single one. But 416 linear feet ÷ 12 = 35 boards if you plan the joints so offcuts get reused in other rows. That's 17 boards saved — a third of the order — from nothing but planning. The calculator shows both numbers so you can see what your board choice really costs.
| Joist size | 12″ o.c. | 16″ o.c. | 24″ o.c. |
|---|---|---|---|
| 2×6 | 10′ 9″ | 9′ 11″ | 8′ 8″ |
| 2×8 | 14′ 2″ | 13′ 1″ | 11′ 0″ |
| 2×10 | 18′ 0″ | 16′ 5″ | 13′ 5″ |
| 2×12 | 21′ 4″ | 19′ 6″ | 15′ 11″ |
Indicative only — species, grade, load and local code all change these. Always verify against your local span tables.
| Board | Actual width | Rows per 12 ft |
|---|---|---|
| 2×4 | 3.5″ | 39 |
| 5/4×6 or 2×6 | 5.5″ | 26 |
| 2×8 | 7.25″ | 20 |
| Size | ft³ | 80 lb bags |
|---|---|---|
| 8″ dia × 36″ | 1.05 | 2 |
| 12″ dia × 36″ | 2.36 | 4 |
| 12″ dia × 48″ | 3.14 | 6 |
| 16″ dia × 48″ | 5.59 | 10 |
| Material | Cost / ft² | Lifespan | Maintenance |
|---|---|---|---|
| Pressure-treated pine | $3–6 | 15–20 yr | Stain/seal every 1–3 yr |
| Cedar | $6–10 | 15–20 yr | Seal every 2–3 yr |
| Redwood | $8–13 | 20–25 yr | Seal every 2–3 yr |
| Composite | $9–17 | 25–30 yr | Wash occasionally |
| PVC | $11–20 | 30+ yr | Wash occasionally |
| Hardwood (ipe) | $15–25 | 40+ yr | Oil annually (or let grey) |
Material only, not installed. Regional prices vary widely — enter your own in the calculator.
100 ft² · 22 rows · 9 joists · 4 posts · ~150 lin ft decking
192 ft² · 26 boards (16 ft) · 13 joists · 6 footings · 676 screws
320 ft² · 35 rows · 16 joists · ~$8–12k in boards alone
Naive: 52 boards. Optimized: 35 boards. Saves 17.
80 ft² · low posts, no stairs — the cheapest build
36″ rise → 5 steps at 7.2″ each · 4 stringers at 48″ wide
480 ft² · composite recommended — no splinters, low upkeep
PT: cheap upfront, ~$3.5k of staining. Composite: cheaper overall.
Everyone shops for decking first, but the frame is the deck. The boards are a wear surface you'll replace one day; the joists, beams, posts and footings are what keep you off the ground for the next thirty years. Get the framing right and a deck is safe for decades. Get it wrong and no amount of expensive composite will save it — deck collapses almost always begin at the ledger or the footings, not the surface.
Joists carry the boards and are typically spaced 16″ on centre. Composite decking usually requires 16″ (and 12″ for diagonal installs) because it's less stiff than wood — check the manufacturer's instructions, because getting this wrong voids the warranty and gives you a bouncy deck. Joists sit on beams, and the beams sit on posts, usually spaced no more than 8 feet apart. Joist size determines how far it can span between supports: a 2×8 at 16″ o.c. reaches about 13 feet, a 2×10 about 16½. Span tables aren't suggestions.
Footings must go below the frost line, or the ground will freeze, expand and lift your deck — a process called frost heave that will tear a deck away from a house over a few winters. The depth varies enormously, from about 12″ in warm regions to 48″ or more in cold ones. A common residential footing is a 12″-diameter pier 36–48″ deep, taking roughly 2.4–3.1 ft³ of concrete each. Your local building department publishes the required depth; ask them before you dig.
Pressure-treated pine is the budget default — cheap, strong, available everywhere — but it needs cleaning and staining every one to three years, and it will check and splinter with age. Cedar and redwood are naturally rot-resistant and beautiful, at a real premium. Composite and PVC cost two to three times as much upfront but need almost nothing beyond an occasional wash. Hardwoods like ipe last forty years, look extraordinary, and will blunt every drill bit you own.
Compare on lifetime cost, not sticker price. A 192 ft² PT deck might cost a fraction of composite in boards — but staining it every two years for 25 years can quietly cost more than the boards did. Run the 25-year comparison in advanced mode: for most people, composite wins on total cost and on the weekends you get back. The counter-argument is real though: if you plan to move in five years, the upfront saving of PT is money in your pocket today.
Board length matters more than people realise. If your deck is 16 ft long, 16 ft boards span it in one piece: no cuts, no waste, no butt joints. Choose 12 ft boards and the lazy approach is two per row — leaving a 4 ft offcut from every board. On a 12×16 deck, that's 52 boards instead of 35. Plan your joints so offcuts get reused elsewhere and you save seventeen boards. The calculator shows both figures because that difference is often hundreds of dollars.
Use coated deck screws rated for treated lumber (which is corrosive to plain steel), or stainless near the coast. Two screws per board at every joist crossing is standard — on a 12×16 deck that's around 676 screws, so buy by the box. Composite decking usually uses hidden fasteners that clip into a groove in the board's edge, giving a clean surface with no visible screws; they cost more and add install time. Joist hangers, structural screws and post bases are not optional hardware; they're what the code inspector will look at first.
Stairs are governed by code and by comfort: risers around 7–7¾″ and treads around 10–11″, and every riser in the flight must be the same height within about ⅜″ — uneven risers are a trip hazard and a common inspection failure. Railings are typically required above 30″ of height, usually 36″ tall, with balusters spaced so a 4″ sphere cannot pass through. These aren't stylistic choices; they're the rules.
Most decks need a permit, and inspections exist because decks fail. The recurring mistakes: attaching the ledger with nails instead of structural screws or bolts (the single most common cause of collapse), skipping flashing behind the ledger so water rots the rim joist, footings above the frost line, posts notched to the point of weakness, joists overspanned, no waste allowance, and buying the wrong board length. Every one is cheap to avoid at the planning stage and expensive — sometimes dangerous — to discover later.
A deck material calculator estimates the number of deck boards, joists, beams, posts, concrete footings, fasteners, stairs and railing parts needed for a deck, based on its dimensions and chosen materials. It produces a bill of materials with quantities, a waste allowance and an estimated total project cost.
Divide the deck width in inches by the board width plus the gap to get the number of rows. A 12 foot wide deck using 5.5 inch boards with a quarter inch gap needs 144 divided by 5.75, which is 26 rows. Multiply by the deck length for total linear feet, then divide by the board length you buy.
Sixteen inches on centre is the standard for most decking. Composite decking often requires 16 inches for perpendicular boards and 12 inches for diagonal installations, so check the manufacturer's instructions. Wider 24 inch spacing is only suitable for certain thick boards and is not recommended for composite. Always follow local code.
Footings must extend below the local frost line, which varies from around 12 inches in warm regions to 48 inches or more in cold climates. A common residential footing is a 12 inch diameter pier 36 to 48 inches deep, holding roughly 2.4 to 3.1 cubic feet of concrete each. Check your local building department.
Composite costs considerably more upfront, often two to three times the price of pressure-treated lumber, but it needs almost no maintenance. Wood requires cleaning and staining every one to three years. Over a 20 to 25 year life the ongoing maintenance often makes composite the cheaper option overall, which this calculator estimates for you.
Materials for a pressure-treated deck commonly run roughly 15 to 25 dollars per square foot, and composite 30 to 60 dollars per square foot. Professional labour typically adds a similar amount again, so a fully installed deck often lands between 30 and 100 dollars per square foot depending on materials, height and complexity.
Choose a board length that divides evenly into your deck length, or long enough to span it in one piece. If boards must be joined, plan the cuts so offcuts are reused in other rows rather than discarded. This calculator compares a simple one-board-per-row count against an optimised plan that reuses offcuts, showing the boards you save.
No. It provides estimates for planning and budgeting only. Joist and beam spans, footing depths, railing heights and fastener requirements are governed by local building codes and site conditions. Decks are structural and a failure can be dangerous. Always confirm your design with local building authorities and a qualified contractor or engineer, and obtain any required permits.
It depends on the span. As a rough guide for southern pine at 16 inches on centre, a 2 by 6 spans about 9 feet 11 inches, a 2 by 8 about 13 feet 1 inch, a 2 by 10 about 16 feet 5 inches, and a 2 by 12 about 19 feet 6 inches. Species, grade and local code all affect this, so always check your local span tables.
Posts are commonly spaced no more than 8 feet apart along a beam, though the exact maximum depends on the beam size, the load and the joist span it supports. Closer spacing means a smaller beam can be used. Every post needs its own footing below the frost line, so post spacing directly determines how many footings you dig.
Two screws per board at every joist crossing is standard. Multiply the number of board rows by the number of joists, then by two. A 12 by 16 foot deck with 26 rows and 13 joists needs about 676 screws, so buy by the box. Use coated screws rated for treated lumber, or stainless steel in coastal areas.
In most jurisdictions yes, especially for raised decks or any deck attached to the house. Permits trigger inspections, which exist because deck failures injure people. Requirements vary by locality and some low, freestanding, ground-level decks may be exempt. Always check with your local building department before starting work.
Around one eighth to one quarter inch is typical, allowing drainage and airflow. Wet pressure-treated lumber shrinks as it dries, so install it with a smaller gap; kiln-dried and composite boards do not shrink, so leave a fuller gap. Composite manufacturers specify exact gaps for both sides and ends, and following them is required for the warranty.
A well built pressure-treated deck lasts around 15 to 20 years, cedar and redwood similar, composite 25 to 30, PVC 30 or more, and hardwoods such as ipe 40 or more. The frame usually outlives the decking surface, so boards are often replaced on an older frame. Maintenance and drainage matter more than the material.
Yes. The share button copies a link that encodes your dimensions, materials and prices, so you can revisit the plan or send it to a contractor or lumberyard. You can also print or save the full bill of materials as a PDF. Everything runs in your browser and nothing is uploaded or stored on a server.