Privacy screen calculator
A slatted screen gives privacy by angle, not by area. Two screens with the same 50% coverage feel entirely different depending on whether the slats are horizontal or vertical, because the gap you can see through is in a different direction.
Your screen
How this is calculated
- Pitch = slat width + gap.
- Horizontal: rows = ⌈height in inches ÷ pitch⌉, and linear feet = rows × length.
- Vertical: boards = ⌈length in inches ÷ pitch⌉, and linear feet = boards × height.
- Closed proportion = slat width ÷ pitch. A 5½″ slat with a 1″ gap closes 85%.
Worked example
12 ft long, 6 ft high, 5½″ horizontal slats, 1″ gap:
- Pitch = 6.5″; rows = ⌈72 ÷ 6.5⌉ = 12 rows
- Linear feet = 12 × 12 = 144 lf
- Closed = 5.5 ÷ 6.5 = 85%
- Framing bays at 8 ft = 2, so three posts and two rails
The same screen with vertical slats would need ⌈144 ÷ 6.5⌉ = 23 boards at 6 ft each — 138 linear feet. Nearly the same material, a completely different view through it.
What a slatted screen actually hides
Horizontal slats hide what is at eye level when you are standing, because the sightline from eye height to a neighbour's window crosses several slats. They do very little for someone standing on a balcony looking down, because that sightline passes through the gaps at a steep angle. Vertical slats do the opposite: they block side views along the screen and let a direct perpendicular view through.
If the goal is a specific neighbour's window, the geometry is worth drawing: the screen angle to that window decides whether the slats hide it. The calculator gives the quantities; the angle is a pencil sketch.
Wind, and why a screen is not a fence
A 15% open screen still passes very little wind compared with an open railing, and it is fixed to a structure rather than embedded in the ground. That makes the connection the weak point: a screen bolted to a deck guard needs the guard to be designed for the added sail area, and a screen on a pergola post loads a member that may only have been sized for its own weight.
Where the screen is tall or the site exposed, spacing the slats wider is a structural decision as well as a visual one.
What a screen calculation cannot know
- It does not check sightlines. Whether the slats hide a particular window depends on geometry this tool does not ask for.
- It does not size the frame or the connections. Wind load on a screen is a real load, and the frame that carries it needs to be designed for it.
- It does not account for slat overlap. Angled or overlapped slats change both the count and the coverage.
- It does not cover fence law. A screen near a property line may be treated as a fence regardless of what you call it.
Questions people actually ask
Horizontal or vertical slats for privacy?
Horizontal blocks eye-level views from nearby windows most efficiently. Vertical blocks views along the screen's length. If the thing you are hiding is at eye level and close, go horizontal.
What gap gives privacy without looking solid?
Around 1″ between 5½″ boards closes 85% and still reads as a screen. Gaps above 2″ start to feel like a trellis and let a lot through at an angle.
How many boards for a 12x6 screen?
With 5½″ boards and a 1″ gap, 12 rows of 12 ft for horizontal — 144 linear feet — or 23 boards at 6 ft for vertical, which is 138 linear feet.
Will a privacy screen block wind?
Substantially, even at 85% coverage, which is why the fixings matter more than the slat count. A screen attached to a guard transfers its wind load into the guard.
Can I attach a screen to a railing?
Only if the railing is designed for it. A guard is sized for a 200 lb point load at the top, not for the sail area of a 6 ft screen in a gust.