Deck Calculator: Materials and Cost Estimate
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- 240 sq ft deck area
- 29 (20 ft) decking boards
- 16 @ 16" joists
Cut list: Deck Calculator: Materials and Cost Estimate
- Deck area240 sq ft
- Decking boards29 x 20 ft (26 rows, 10% waste)
- Fasteners874 screws, 3 boxes of 350
- Joists16 2x10 at 16 in, spanning 12.0 ft
- Beam2-ply 2x10
- Posts and footings4 6x6 posts, 22 bags of 80 lb concrete
- Railing44 ft, 9 posts, 106 balusters under 4 in apart
- Estimated cost$3,400 ($14 per sq ft)
- Same deck inPressure-treated $3,400, cedar $4,942, composite $6,182
- [ ] Decking: Pressure-treated boards, 5.5 in x 20 ft29, $928
- [ ] Decking: Deck screws (350 per box)3 boxes, $135
- [ ] Framing: 2x10 joists, 12 ft16, $403
- [ ] Framing: 2x10 rim and band boards44 linear ft, $92
- [ ] Framing: 2x10 ledger with flashing and 30 lag screws20 ft, $117
- [ ] Framing: 2-ply 2x10 beam40 linear ft, $84
- [ ] Framing: Joist hangers and hurricane ties32, $64
- [ ] Framing: 2x10 mid-span blocking15, $42
- [ ] Foundation: 6x6 posts with bases and caps4, $280
- [ ] Foundation: 80 lb concrete for footings22 bags, $154
- [ ] Railing: Railing, 9 posts, 106 balusters44 linear ft, $1,100
- [ ] Decking boards, 20 ft, 5.5" wide
- [ ] 2x10 pressure-treated joists
- [ ] Pressure-treated beam stock, 12 ft
- [ ] 6x6 posts, ground contact
- [ ] Joist hangers and hanger nails
- [ ] Exterior deck screws
- [ ] Concrete mix, 80 lb
- [ ] Joist tape
Need the beam, post or footing size? Use the deck beam span calculator and the deck footing size calculator. Concrete per hole is in the sonotube calculator, stair cuts in the stair stringer calculator, and baluster gaps in the spacing calculator.
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20 x 12 ft deck
A 240 sq ft deck framed with 16 2x10 joists at 16 in on center over 4 posts, decked with 27 boards 5.5 in wide. Plan assumes a low deck; attached or tall decks need a permit and inspected footings.
- Materials
- $3,400
- Time
- 2 weekends
- Level
- Advanced
- 1
Permit, design, and utility locate
Most towns require a permit for a deck over 30 in high or attached to the house, with footing and framing inspections. Draw your 20 x 12 ft plan, confirm joist span tables for 2x10 at 16 in, and call 811.
- Apply for a permit if required
- Check span tables for your lumber
- 811 utility locate
- 2
Lay out and square
Set batter boards and strings for the outline. Square the corners with 3-4-5 and match the diagonals. Mark the post locations along each beam line.
- Strings at finished height
- Diagonals equal
- Mark 4 footing locations
- 3
Dig and pour footings
Dig 4 holes below frost depth, or to the depth your permit specifies, and pour the footings (22 bags in all) with post bases set in the wet concrete. Schedule a footing inspection before the pour if required.
- Holes below frost line
- Footing inspection if required
- Post bases aligned to the string
- Deck area
- 240 sq ft
- Decking boards
- 29 (20 ft)
- Joists
- 16 @ 16"
- Est. cost
- $3,400
8 steps · 9 tools · 8 materials
5 more steps, the full tool list and a shopping list you can check off as you go.
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3/520 x 12 ft deck
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12 x 16 deck materials list
An attached 12 x 16 ft pressure-treated deck, 3 ft high, 16 in joists, 5-1/2 in boards and a 3-sided railing:
| Item | Quantity | Cost |
|---|---|---|
| Decking: Pressure-treated boards, 5.5 in x 16 ft | 29 | $742 |
| Decking: Deck screws (350 per box) | 3 boxes | $135 |
| Framing: 2x10 joists, 12 ft | 13 | $328 |
| Framing: 2x10 rim and band boards | 40 linear ft | $84 |
| Framing: 2x10 ledger with flashing and 24 lag screws | 16 ft | $100 |
| Framing: 2-ply 2x12 beam | 32 linear ft | $90 |
| Framing: Joist hangers and hurricane ties | 26 | $52 |
| Framing: 2x10 mid-span blocking | 12 | $34 |
| Foundation: 6x6 posts with bases and caps | 3 | $210 |
| Foundation: 80 lb concrete for footings | 21 bags | $147 |
| Railing: Railing, 8 posts, 96 balusters | 40 linear ft | $1,000 |
Total about $2,921, or $15 per sq ft.
How much decking for common deck sizes
| Deck | Boards | Joists | Posts | Pressure-treated | Composite |
|---|---|---|---|---|---|
| 10 x 10 ft | 25 x 10 ft | 9 2x8 | 3 | $1,871 | $3,346 |
| 12 x 12 ft | 29 x 12 ft | 10 2x10 | 3 | $2,373 | $4,282 |
| 12 x 16 ft | 29 x 16 ft | 13 2x10 | 3 | $2,921 | $5,266 |
| 16 x 20 ft | 38 x 20 ft | 16 2x12 | 4 | $4,439 | $7,943 |
| 20 x 20 ft | 48 x 20 ft | 16 beam | 4 | $5,150 | $9,434 |
How the math works
- Count the board rows. Divide the deck depth in inches by the board width plus the gap. 12 ft at 5-1/2 in boards with a 3/16 in gap is 26 rows.
- Pick a board length. Use boards that match the deck length, or ones that split it evenly, so butts land on joists. Add 10% waste (18% for diagonal).
- Count the joists. Joists run out from the house and are counted along it: length in inches / spacing + 1. A 20 ft deck at 16 in takes 16 joists.
- Size the joists and beam. Read the joist size from the span table for the deck depth, then the beam and post spacing from IRC Table R507.5.
- Add footings, railing and stairs. One footing per post, about 4 to 6 bags of concrete each, a railing post every 6 ft and balusters under 4 in apart.
| Joist | 12 in on center | 16 in | 24 in |
|---|---|---|---|
| 2x6 | 9'11" | 9'0" | 7'7" |
| 2x8 | 13'1" | 11'10" | 9'8" |
| 2x10 | 16'2" | 14'0" | 11'5" |
| 2x12 | 18'0" | 16'6" | 13'6" |
Beam and post sizes come from the deck beam span calculator, and footing sizes from the deck footing size calculator.
Waste factors and permits
| Pattern | Waste to add |
|---|---|
| Straight, boards match the deck length | 5 to 10% |
| Straight with butt joints | 10% |
| Diagonal | 15 to 20% |
| Picture frame or herringbone | 20 to 25% |
Pull a permit for anything attached to the house or over 30 in high, call 811 before digging, and keep the deck building cheat sheet handy for ledger flashing and inspection order. Need stairs off the deck? Get the rise and run from the stair calculator and the stringer layout from the stair stringer calculator; the piers come from the sonotube concrete calculator. Refinishing an existing deck instead? See how to refinish a deck.
Deck calculator FAQ
How many deck boards do I need for a 12x16 deck?
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How many joists for a 12x20 deck?
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