How to estimate a fence or deck
This calculator works in two modes. Pick Fence to count pickets for a run of privacy or picket fence, or Deck to count deck boards, joists, and posts for a rectangular deck. Enter your dimensions and the tool returns a buyable material count plus an estimated cost.
Fence: picket spacing math
The number of pickets depends on how wide each board is and how much gap you leave
between boards. Each picket effectively occupies its own width plus one gap, so
the spacing per picket is picketWidth + gap.
- Spacing (in) = picket width + gap
- Pickets = (fence length × 12) ÷ spacing
A standard dog-ear picket is 5.5 inches wide. With a 0.5 inch gap, each
picket takes up 6 inches, so a 50-foot fence needs (50 × 12) ÷ 6 = 100 pickets
before waste. Tighten the gap for more privacy and you will need more boards;
widen it for an open, airy look and you will need fewer.
Deck: board, joist, and post math
A deck is three separate counts that all start from the deck footprint.
- Deck area (ft²) = length × width
- Boards = deck area ÷ coverage per board
- Joists = floor((length × 12) ÷ joist spacing) + 1
- Posts = perimeter ÷ post spacing, where perimeter = 2 × (length + width)
Board coverage is the square footage one board covers — a 6 in × 8 ft board
covers about 4 ft². Joists are spaced by their on-center distance (commonly
16 inches), and the + 1 accounts for the joist at the very end of the run.
Posts are spread around the perimeter at the spacing your beam and footing plan
allows, usually 6 to 8 feet.
Common mistakes to avoid
- Forgetting the gap in fence math. Dividing by picket width alone overstates the count. Always add the gap to the picket width first.
- Skipping the end joist. Joist spacing tells you the number of bays, not the number of joists — there is always one more joist than bays.
- Under-counting posts. Corners, stairs, and longer beam spans often need extra posts beyond a simple perimeter divide. Treat the post count as a starting point.
- Ignoring waste. Add 10% for saw cuts, defects, and trimmed ends. The calculator builds this into the board counts.
Estimating cost
The cost shown adds up pickets (fence) or deck boards, joists, and posts (deck) at national-average unit prices. It is a material estimate only and excludes concrete for footings, fasteners, railings, stairs, joist hangers, delivery, and labor. Lumber prices move quickly, so adjust the unit price to match a local quote before you order.