Deck & Fence Material Estimator
Pick your project and enter the dimensions — the estimator counts boards, joists, pickets, rails, and posts.
Runs entirely in your browser — your numbers never leave this page.
How it works
Deck and fence estimating is just division with round-ups — you can't buy half a board, so every count rounds up. The estimator handles the two projects separately:
Deck boards = ceil(Width (in) ÷ 5.75) — a 5.5-in board plus a ¼-in gap
Joists = floor(Width (in) ÷ 16) + 1 — 16 inches on-center
Pickets = ceil(Fence length (in) ÷ picket width)
Rails = ceil(Length ÷ 8) × 2 — two 2×4 rails per 8-ft section
- Deck boards run the deck's length; the count covers the width. Buy boards at the full deck length to avoid butt joints — or plan joints to land on joists.
- Joists sit 16 inches on-center for standard decking (12 in OC if you use diagonal decking or composite).
- Posts go every 6 ft around a deck perimeter, every 8 ft along a fence — plus one extra at the end of the run.
- Fence pickets assume a privacy style with boards butted tight. For a spaced picket fence, add your gap to the picket width before dividing.
- Screws: two per board at every joist crossing — it adds up fast, so buy the 5-lb box.
Frequently asked questions
What gap should I leave between deck boards?
About ¼ inch for pressure-treated wood — it shrinks as it dries, so a tight install opens up on its own. Composite decking follows the manufacturer's gap (usually 3/16–¼ in) and barely moves.
How far apart should deck joists be?
16 inches on-center is standard for wood decking. Go 12 inches on-center for diagonal decking patterns, composite boards, or hot tubs — anything that needs a stiffer floor.
How deep should deck and fence posts go?
Below your local frost line — typically 30–48 inches depending on climate. A post that stops above the frost line will heave every winter. Set posts in concrete and crown the concrete so water drains away.
How many rails does a fence need?
Two 2×4 rails per 8-foot section for fences up to 6 ft tall. For 7–8 ft fences, use three rails to stop the pickets warping — add 50% to the rail count.
Pressure-treated vs cedar — which should I choose?
Pressure-treated pine is cheapest and lasts 15–20 years with maintenance. Cedar costs roughly twice as much, looks better, and resists rot naturally. Both need a water-repellent sealer every 2–3 years.
How much concrete per fence post?
One 50-lb bag per 4×4 post in a 10-inch hole is the rule of thumb (about 0.375 cu ft). For gate posts or soft soil, go bigger — a wobbly gate post ruins the whole fence.
Should pickets touch or have a gap?
Privacy fences butt pickets tight — they shrink and open small gaps naturally. Spaced picket (picket-style) fences use a 2–4 in gap; add the gap to the picket width in the estimator math.
Do I need a permit for a deck or fence?
Usually yes for a deck, sometimes for a fence over 6 ft. Rules are local — check setbacks, footing depth, railing height (typically 36 in), and HOA rules before buying lumber.
Why does the estimator add one extra post?
Posts land every 8 ft plus one at the end of the run — a 16-ft fence needs posts at 0, 8, and 16 ft. Forgetting the last post is the classic fence-math mistake.
What about gates, stairs, and railings?
This estimator covers the field materials. Plan gates (framing + hinges + latch), deck stairs (stringers + treads), and railings (balusters + top rail) as separate mini-projects with their own counts.