Shade Sail Size Calculator
Plan a tensioned shade sail: fabric size, attachment layout, post heights, hypar twist, hardware, shade performance and cost — 3-point triangle or 4-point square/rectangle.
Frequently asked questions
What size shade sail do I need for a 16×12 ft patio?
Order a sail measured 17.2 × 12.9 ft corner-to-corner (about 222 ft² of fabric) to shade a 16 × 12 ft area. Your attachment points then sit at 20.2 × 15.9 ft eye-to-eye, leaving a 1.5 ft hardware gap at each corner for turnbuckles. For rectangles, measure both diagonals — here 25.7 ft each — to verify squareness before ordering.
Why is the sail smaller than the distance between my posts?
Two reasons. First, sail edges are cut with a catenary curve — typically about 7% of the side length, the industry standard — so the effective shade is smaller than the corner-to-corner size (a 16 ft side shades like roughly 14.9 ft). Second, leave a 1–2 ft gap between each sail corner and its anchor point for tensioning hardware; the fabric stretches and needs re-tensioning room.
How deep should shade sail post footings be?
Bury one-third of the total post length in concrete — footings are mandatory, not optional. For a 7 ft attachment height with posts leaning 7.5°, each low post needs a 3.53 ft deep, 12-inch-diameter footing: about 2.77 ft³ of concrete, or five 80-lb bags. Call 811 before you dig.
Why do shade sail posts lean, and by how much?
Lean each post 5–10° away from the sail so the post resists the inward pull of the tensioned fabric instead of being dragged toward it. At 7.5° of lean, a 7 ft attachment height needs 7.06 ft of post above ground; the footing still follows the one-third rule (3.53 ft deep here).
What is a hypar twist, and how do I plan it?
Hypar (hyperbolic paraboloid) means setting diagonally opposite corners high and the other diagonal low, twisting the fabric into a saddle. The industry rule of thumb: twist = 15% of the longest side for a gentle look (up to 20% for dramatic). For a 17.2 ft side with 7 ft low points, the twist is 2.58 ft, so the high corners attach at 9.58 ft. The twist tensions evenly and sheds rain toward the two low corners.
How much slope does a shade sail need so rain runs off?
Steeper is better — around 20–30° is the practical range. But slope costs height fast: a 20° slope across a 20.2 ft span rises 7.35 ft, putting the high side at 14.35 ft, which this calculator flags as a pro-install job. A hypar twist (mode 4) achieves drainage with far less height.
What hardware do I need for a 4-corner shade sail?
Per corner: one turnbuckle (12-inch for sails over 200 ft², 8-inch below), one D-ring (usually pre-installed on the sail), and one carabiner or snap hook — so four of each here. Add pad eyes for each wall attachment, about 10 ft of rope or chain total (1.5 ft gap + 1 ft slack per corner), and twenty 80-lb concrete bags for the four post footings.
How much UV does a 93% shade sail really block when the sun is at 60°?
About 91.9% — oblique sun pushes more UV through the weave (8.1% transmitted vs 7% overhead). The sail’s ground footprint is about 208.6 ft² at a 20° slope, and the shadow shifts about 6.16 ft sideways from directly under the sail at roughly 10.7 ft average height, so plan seating for the afternoon shadow position.
How much does a 16×12 ft shade sail project cost?
Mid-tier DIY: about $943 (planning range $849–$1,085). Breakdown: fabric $355.18, four steel posts $340, twenty concrete bags $140, four turnbuckles $48, rope/chain and carabiners $60. Pro installation adds roughly $500 plus $75 per post.
Should I choose a triangle or a rectangle shade sail?
Triangles fit awkward spaces and tension easily with three anchors; rectangles and squares cover more area per corner count but need four anchors and careful diagonal cross-checking. Only a 4-point sail can use a true hypar twist. For broad rectangular pads like patios and dining areas, a 4-point sail usually wins; for narrow or odd corners, go triangle.
Free tool by NRTechStudio