Deck Calculator
Estimate decking boards, joists, posts, fasteners, and total material cost for a deck build.
Your details
Materials
Cost
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Estimated material cost
$4,549
$24 per square foot over 192 ft²
Includes your inputs, the full breakdown, and every row of the table.
Decking needed
458 linear ft
26 rows × 16.0 ft
Joists
13 at 12.0 ft
16" on center
Posts & footings
6
Deck screws
~2,197
Two per board per joist
- Deck area
- 192 ft²
- Decking (458 lf incl. 10% waste)
- $1,464
- Framing (250 lf)
- $525
- Railing (40 lf)
- $2,200
- Hardware, hangers & footings
- $360
- Total materials
- $4,549
- With labor (roughly 2×)
- $9,098
What this means
- At 16" on center you need 13 joists. Composite decking generally requires 16" maximum, and 12" for diagonal patterns.
- Board lengths come in even increments — 8, 12, 16, and 20 feet. Planning your deck dimensions around those lengths dramatically reduces waste and the number of butt joints.
- This covers materials only. Professional labor typically doubles the total, and permits, stairs, and footings below the frost line add more.
How the deck calculation works
A deck estimate has three material groups: the decking surface, the frame beneath it, and the railing. Decking is calculated by dividing deck width by the effective coverage of one board — its actual width plus the gap — to get the number of rows, then multiplying by deck length.
Joist spacing determines both cost and feel. Sixteen inches on center is standard for pressure-treated lumber laid perpendicular. Most composite manufacturers require sixteen inches maximum and twelve inches for diagonal installations, since composite is less stiff than wood.
Frequently asked questions
How much does it cost to build a deck?
Materials for a pressure-treated deck run roughly $15-25 per square foot; composite runs $30-60. Professional installation typically doubles the total.
What gap should I leave between deck boards?
About 3/16 inch for kiln-dried lumber and composite. Wet pressure-treated boards shrink as they dry, so they can be installed nearly tight and will open up on their own.
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Disclaimer. This calculator is provided for general information and educational purposes only and does not constitute financial, tax, legal, medical, or engineering advice. Results are estimates based on the inputs you provide and the assumptions described above. Confirm any figure with a qualified professional before acting on it.