Hardscape calculator
Deck calculator: boards, joists, footings and cost
One deck, one set of numbers. Enter the size and the material and this deck building calculator returns the board count, the framing, the footings, the fasteners and what the whole thing costs.
Your project
The dimension the deck boards run along — usually the side parallel to the house.
Joists run this way, so this is the number that has to fit the joist span table.
Material changes price and maintenance, not board count — every option here is a 5.5 inch face.
Buying boards that span the full deck length removes every butt joint and most of the waste.
16" on centre is the standard. Composite laid diagonally needs 12".
Anything over 30 inches needs guard rail, and that changes the cost more than the size does.
Crews typically order 5-10% extra to cover compaction, spillage and uneven subgrade.
Deck boards needed
27
boards at 16 ft · 192 sq ft deck · includes 5% waste
- Deck area
- 192 sq ft
- Linear feet of decking
- 421 lin ft
- Joists at 16" on centre
- 13 × 12 ft
- Joist lumber
- 156 lin ft
- Beam posts and footings
- 3 posts
- Rim / ledger board
- 56 lin ft
- Joist hangers
- 26 hangers
- Deck screws (approx)
- 633 screws
- Guard rail required
- 40 lin ft
- Decking material cost
- $884
- Installed cost estimate
- $8,384
Board count assumes boards run the length of the deck with a 1/4 inch gap. Framing figures are planning quantities — the joist size and beam span still have to be checked against your local code and the span tables below.
The shareable link reopens this calculator with your exact inputs.
How many deck boards do I need?
Deck area divided by the coverage of one board. A 5/4x6 or 2x6 board measures 5.5 inches across, and with the standard quarter-inch gap each board covers 5.75 inches — 0.479 feet — of width per foot of length. So a 16 by 12 foot deck of 192 square feet needs about 401 linear feet of decking, which is 25 sixteen-foot boards plus waste.
Order in the longest length that spans your deck. Butt joints are the weak point of a deck surface: they need blocking underneath, they collect water, and they are where rot starts. A 16 foot deck framed for 16 foot boards has no joints at all in the field.
Add five to ten percent for waste. Straight runs are close to five; diagonal layouts throw away fifteen percent in angle cuts, and a picture-frame border eats another eight.
Framing is what the deck actually stands on
Joists run perpendicular to the decking, at 16 inches on centre for almost every wood deck. Composite is the exception — most manufacturers require 16 inches for a straight lay and 12 inches on the diagonal, because the boards flex between supports in a way timber does not.
Joist count is the deck length in inches divided by the spacing, plus one for the closing joist. The joist size then has to carry the span: a 2x8 reaches about 11 feet 11 inches at 16 inch spacing, a 2x10 about 14 feet 7 inches. Going one size up is nearly always cheaper than adding a beam line and another row of footings.
Every joist needs a hanger at each end, and every hanger needs the structural screws or nails the manufacturer specifies. Ordinary deck screws in a joist hanger are a code failure and a real structural one.
What a deck costs to build
Pressure-treated decks land around $25 to $35 per square foot installed, cedar $30 to $45, composite $35 to $55 and PVC or tropical hardwood $45 to $70. The board itself is only about a quarter of that — framing, footings, fasteners, railing and labour are the rest.
Railing is the line item that surprises people. At $40 to $150 per linear foot, a rail around three sides of a 16 by 12 deck can add $3,000 to $6,000, which is frequently more than the decking. If the deck sits under 30 inches above grade, most codes do not require a guard, and skipping it changes the budget completely.
Doing it yourself saves the labour share — roughly half the total. The savings are real, but so is the inspection: pulling a permit and having the footings and framing inspected is what makes the deck insurable and sellable.
Deck boards needed by deck size
5.5 inch boards with a 1/4 inch gap, before waste.
| Deck size | Area | Linear feet | 16 ft boards | 12 ft boards |
|---|---|---|---|---|
| 8 × 10 ft | 80 sq ft | 167 | 11 | 14 |
| 10 × 12 ft | 120 sq ft | 250 | 16 | 21 |
| 12 × 12 ft | 144 sq ft | 301 | 19 | 26 |
| 16 × 12 ft | 192 sq ft | 401 | 26 | 34 |
| 16 × 16 ft | 256 sq ft | 534 | 34 | 45 |
| 20 × 16 ft | 320 sq ft | 668 | 42 | 56 |
| 24 × 16 ft | 384 sq ft | 801 | 51 | 67 |
Decking material, price and life
Delivered board price and typical installed cost including framing and labour.
| Material | $ / lin ft | $ / sq ft installed | Life (years) | Notes |
|---|---|---|---|---|
| Pressure-treated pine (5/4x6) | $2.10 | $27 | 10-15 | Cheapest board on the rack; needs cleaning and sealing every two to three years. |
| Western red cedar | $3.20 | $33 | 15-20 | Naturally rot resistant, soft underfoot, greys out within a season unless sealed. |
| Redwood | $4.50 | $38 | 20-25 | Best-looking softwood, priced accordingly and mostly a West Coast option. |
| Capped composite | $4.80 | $42 | 25-30 | No sealing, 25-year warranties, but runs hot in full sun and sags at 24 inch spacing. |
| Cellular PVC | $6.50 | $50 | 30-50 | Lightest and most stain-proof, and the only board that will not rot at ground contact. |
| Ipe / tropical hardwood | $7.50 | $58 | 40-75 | Hardest wearing surface available; pre-drilling every fastener is mandatory. |
Frequently asked questions
+How many deck boards do I need for a 12x16 deck?
About 401 linear feet of 5.5 inch decking, which is 25 boards at 16 feet or 34 at 12 feet, before waste. Add five to ten percent and order 27 sixteen-footers.
+How do I calculate deck boards?
Multiply length by width for the area, then divide by 0.479 — the square feet one linear foot of 5.5 inch board covers with a quarter-inch gap. Divide the linear feet by the board length you are buying to get the board count.
+How far apart should deck joists be?
16 inches on centre for wood decking laid straight. Composite usually requires 16 inches straight and 12 inches on a diagonal. 24 inch spacing is only acceptable with 2x6 wood decking and is not worth the bounce.
+How much does it cost to build a 12x16 deck?
Roughly $5,000 to $7,000 in pressure-treated pine installed, $7,000 to $10,000 in composite, before railing. Building it yourself typically halves that, since labour is about 50% of a deck contract.
+Do I need a permit to build a deck?
In nearly every jurisdiction, yes, for any deck attached to the house or more than 30 inches above grade. The inspection usually happens twice: once with the footing holes open, once with the framing exposed.
+How many footings does a deck need?
One per beam post, with posts no more than 8 feet apart on a standard 2-ply beam. A 16 foot deck attached at the ledger needs three footings along the outer beam; a freestanding deck needs a second row.
+Should deck boards run parallel or perpendicular to the house?
Parallel to the house is standard, because joists then run out from the ledger and drain water away from the wall. Running boards perpendicular means the joists run parallel to the house, which needs a different beam layout.