How to measure for a new deck
Measure the length along the wall of the house and the depth straight out from the house, both in feet. Use the outside edge of the finished deck, not the footprint of the posts, which are usually set back from the edges. For an L-shaped or wraparound deck, split it into rectangles, run the calculator once for each, and add the results.
The calculator assumes a common layout: joists run out from the house (so each joist is as long as the deck is deep) and deck boards run parallel to the house. If you plan a diagonal or picture-frame pattern, raise the waste allowance to about 15% and expect more joist blocking.
Worked example: a 16 × 12 ft pressure-treated deck
With the default inputs (16 ft along the house, 12 ft deep, 5.5 in boards in 16 ft lengths, joists 16 in on center, railing on three sides, national average prices):
| Item | Calculation | Result |
|---|---|---|
| Area | 16 × 12 | 192 sq ft |
| Board rows | 144 in ÷ (5.5 in + 0.1875 in gap) = 25.3 | 26 rows |
| Boards per row | 16 ft ÷ 16 ft boards | 1 |
| Boards to buy | 26 × 1 × 1.10 = 28.6 | 29 boards |
| Joists | (192 in ÷ 16 in) + 1 | 13 joists, 12 ft each |
| Deck screws | 192 × 350 ÷ 100 | 672 screws (2 boxes of 350) |
| Railing | 16 + 12 + 12 | 40 lin ft |
| Hire a pro | 192 × $25–$50 + 40 × $30–$80 | $6,000 – $12,800 |
| DIY materials | 192 × $10–$20 + 40 × $15–$40 | $2,520 – $5,440 |
Choosing a board length that matches or divides evenly into your deck length matters. The same deck with 12 ft boards needs two boards per row, which means a butt joint in every row that has to land on a joist, plus 4 ft offcuts you may not be able to use.
Comparing decking materials
For the same 192 sq ft surface, the 2026 national ranges give:
| Material | Hire a pro | DIY materials |
|---|---|---|
| Pressure-treated | $4,800 – $9,600 | $1,920 – $3,840 |
| Cedar | $5,760 – $9,600 | $1,920 – $3,840 |
| Composite | $7,680 – $15,360 | $3,072 – $6,144 |
Those figures cover the deck surface and framing, not the railing. Cedar materials land in the same range as pressure-treated in the source data, but the cedar boards themselves make up roughly half of that ($5–$10 per sq ft), so the board grade you choose moves the price a lot.
What drives the price
- Material: composite’s installed range starts about where pressure-treated tops out.
- Height and footings: a low deck on a flat yard needs short posts and simple footings. A second-story deck needs taller posts, beams, more bracing and often engineered drawings.
- Railing: on the example deck, railing adds $1,200–$3,200 to a pro install. That is an editorial estimate; aluminum, cable and glass railings can cost well beyond the top of that range.
- Joist spacing: tighter spacing (12 in) adds joists, but it is often required for composite boards and diagonal patterns. Wider spacing saves lumber only if your decking is rated for it.
- Local cost level: the regional setting multiplies every line, from 0.85× in low-cost areas to 1.4× in the most expensive metros.
DIY vs hiring a contractor
The DIY figure counts materials only. On top of that, plan for tool rentals (post-hole auger, miter saw, possibly a concrete mixer), the permit fee, and time: framing is the slow part, and the ledger connection and footings are the structural details inspectors check most closely. Many owners hire out the framing and footings, then install the decking and railing themselves.
What’s not included
Stairs (use the stair stringer calculator), concrete footings (see the concrete calculator), joist hangers and structural hardware, flashing tape, removal of an old deck, lighting and built-in benches. If you are also fencing the yard, the fence cost calculator uses the same regional cost levels so the two estimates line up.
How this calculator works
- Area = length × depth. Installed cost = area × installed price per sq ft × local cost factor; DIY cost uses the material-only price per sq ft.
- Board rows = ceil(depth in inches ÷ (board width + 0.1875 in)); boards per row = ceil(length ÷ board length); boards = rows × boards per row × (1 + waste), rounded up.
- Joists = ceil(length in inches ÷ spacing) + 1, each as long as the deck depth.
- Railing length = length + 2 × depth for three sides, or length + depth for two sides.
Assumptions and limitations
- Deck boards run parallel to the house and joists run out from the house, spanning the deck depth.
- Boards are spaced with a 3/16 in (0.1875 in) gap; actual gaps depend on the material and its moisture content.
- Screw count is an editorial estimate of about 350 deck screws per 100 sq ft for face-screwed boards. Hidden fastener systems use clips instead.
- Railing cost is an editorial estimate of $30–$80 per linear foot installed; DIY railing material is assumed to be half of that. Stair openings and gates are not deducted.
- Installed and material prices are national 2026 per-square-foot ranges that include framing; the local cost level multiplies every line.
- Stairs, footings for tall decks, permits, demolition of an old deck and built-ins are not included.
These results are planning estimates, not quotes. Local prices, site conditions and building codes vary, so get written estimates from licensed contractors before you commit to a budget.
Try your own numbers. Every price and assumption above is editable in the estimator.
Back to the deck cost estimatorFrequently asked questions
Is composite decking worth the extra cost?
Should joists be 12, 16 or 24 inches apart?
Do I need a permit to build a deck?
Sources and data
- HomeGuide (2026) — pressure treated decking cost
- HomeGuide (2026) — cedar decking cost
- HomeGuide (2026) — composite decking prices
Prices are US national ranges reviewed October 2026 (data version 2026.10). A few values are editorial estimates where no single published source exists; the Cost Index marks each one. Read our methodology and editorial policy.