| Shape | Inputs | Area (sq m) | Allowance | Fabric (sq m) |
|---|---|---|---|---|
| Triangle | a=4.0, b=5.0, c=6.0 | 9.922 | 10% | 10.914 |
| Rectangle | L=3.0, W=2.5 | 7.500 | 8% | 8.100 |
| Trapezoid | b1=4.8, b2=3.6, h=2.2 | 9.240 | 12% | 10.349 |
| Time | Shape | Area | Fabric |
|---|---|---|---|
| No calculations saved yet. | |||
- Rectangle / Square: Area = Length × Width.
- Right Triangle: Area = ½ × Leg A × Leg B.
- Triangle (three sides): Heron’s formula: s = (a+b+c)/2, Area = √(s(s−a)(s−b)(s−c)).
- Trapezoid: Area = ((Base1 + Base2) / 2) × Height.
- Custom Coordinates: Shoelace method for polygon area from points (x,y).
Effective shade: Effective area = Area × Shade factor%.
- Select the sail shape that matches your garden layout.
- Choose meters or feet, then enter your measurements.
- Add an allowance percent for hems and tensioning.
- Optional: set a shade factor and cost rate for budgeting.
- Press Calculate to view results above the form.
- Use CSV/PDF buttons to save or share your results.
Sizing for Comfort Zones
Shade sails can cool a patio, seedling bench, or seating corner by reducing direct solar gain. Use the calculated area to match the space you actually occupy, not the whole yard. For dining sets, add clearance around chairs and walk paths. For plant beds, prioritize midday coverage and leave edges open for airflow. Record your target coverage before choosing posts and anchor points. Measure between anchors at working height, then confirm diagonal spans to reduce installation surprises. before cutting any posts.
Choosing Shapes for Garden Geometry
Triangular sails fit tight corners and work well between three posts or walls. Rectangles cover long borders and pergola-like zones, but need stronger tension on each side. Trapezoids help when posts are not perfectly aligned, such as along fences with setbacks. Custom coordinates are useful for irregular courtyards; enter measured points to capture real geometry and avoid ordering fabric that cannot be tensioned cleanly.
Allowance and Hardware Planning
Fabric area includes a controllable allowance for hems, corner reinforcement, and tensioning hardware. Many installers add 5–15% depending on edging style and turnbuckle travel. Higher wind exposure may require heavier webbing and more reinforcement, which can increase effective material use. Use the perimeter output to estimate cable, rope, or binding length, then add extra for terminations and adjustment.
Shade Factor and Sun Path Reality
Effective shade is rarely 100% all day. Sun angle changes with season, and a sloped sail can shift shadow across beds. Set a shade factor of 70–90% to model gaps from posts, hardware, and unavoidable edge lift. If you plan a steep pitch for rain runoff, expect a smaller midday footprint. Compare several factors to see how much usable shade you will get.
Budgeting and Material Selection
The cost estimate multiplies fabric area by your chosen rate, letting you compare woven polyethylene, HDPE mesh, and coated fabrics. Mesh often shades while allowing breezes, which benefits humidity-sensitive plants. Coated fabric blocks more sun and rain but can trap heat. Use the saved history to test options, then export a CSV for supplier quotes and a PDF for installers.
FAQs
Which measurements should I take first?
Start with planned anchor locations, then measure the straight-line distances between them. For triangles, measure all three sides. For rectangles, measure length and width. Recheck with a tape at the same height where hardware will sit.
What allowance percent is typical for a garden sail?
Most DIY installs use 8–12% for hems, corner patches, and tension adjustment. Use lower values for pre-finished sails and higher values for custom sewing, large turnbuckles, or added reinforcement in windy gardens.
Why does the triangle option require three sides?
Three sides let the calculator use Heron’s formula, which works for any triangle shape. It also validates the triangle inequality so you avoid impossible dimensions that cannot be tensioned into a real sail.
When should I use custom coordinates?
Use coordinates when your anchors form an irregular polygon, such as a courtyard with multiple walls. Enter points in order around the perimeter. The shoelace method estimates area and perimeter from those points without guessing shape.
How do I choose a shade factor?
Use 100% for ideal, flat coverage. Choose 80–90% when you expect edge gaps, steep pitch, or partial obstruction from posts and fittings. Compare a few values to see how usable shade changes seasonally.
Does the cost estimate include hardware and posts?
No. It estimates fabric cost based on the allowance-adjusted area and your rate. Add separate line items for posts, anchors, turnbuckles, cables, and installation. Use the perimeter output to help size edging and cabling.