What size shade sail do I need? A measuring guide
Altisafe Pro
The most common shade sail mistake is buying a sail the same size as the space you want to cover. A sail is never fitted taut across its exact span — it needs room at each corner for the tensioning hardware, and slack to be pulled tight afterwards. Order to the span and it will not fit.
Here is how to measure properly before you order.
Measure the fixing points, not the patio
Start from where the sail will actually attach, not from the edge of the area you want shaded. Your fixing points might be a wall, a post, a pergola beam or a mature tree, and they are rarely a neat rectangle around the space.
Measure the distance between each pair of fixing points, corner to corner around the shape. Write all of them down — on a four-point install you need four side measurements, and it is worth measuring the two diagonals as well, because a patio that looks square usually is not.
Then take the allowance off
Allow roughly 30 to 40 cm at each corner for the tensioner, shackle or turnbuckle that connects the sail to the fixing point. That hardware sits between the sail's corner ring and your anchor, and it has to have room to do its job.
So on a span of 4 m between two posts, you are looking for a sail closer to 3.2 to 3.4 m on that side, not 4 m.
If you are between two sizes, size down
A sail slightly too small is solved with a longer turnbuckle or an extra shackle. A sail slightly too big cannot be tensioned at all — and an untensioned sail flaps, wears at the seams and collects water.
Choosing the shape
The shape follows your fixing points, not the other way round.
- Rectangular — the usual choice over a dining table, a lounge setting or a deck, where you want maximum coverage from four anchors.
- Triangular — better where you only have three solid anchors, or where you want to shade one corner of a yard. Two triangles overlapped at different heights also shed water and wind better than a single large square, and look far more deliberate.
- Triangular with integrated lighting — the same job, with the evening covered. Worth considering over a table you use after dark.
You can see the shapes in the shade sail range.
Breathable or waterproof?
This decides comfort more than any other choice, and it is regularly got wrong.
Breathable HDPE
A knitted fabric that lets hot air escape upward instead of trapping it underneath. It also lets wind pass through, which puts far less load on your fixing points. For shading a patio or a pool through an Australian summer, this is usually the right answer.
It is not waterproof. Light rain will come through.
Waterproof polyester
Keeps rain off, which is what people think they want. The trade-off is that it traps heat underneath and catches wind like a sail on a boat — because that is exactly what it is. It needs stronger fixing points and a steeper pitch so water runs off rather than pooling.
Choose it only if you genuinely need rain cover. If you want shade, breathable is more comfortable and easier to install.
Your fixing points have to take real load
A tensioned sail pulls hard, and it pulls harder in wind. Before you order, look honestly at what you are attaching to:
- A masonry wall — reliable, with the right fixings for the substrate.
- A solid post — fine if it is set properly. A post that wobbles now will lean within a season.
- A mature tree — workable, but a living anchor that moves; allow for it.
- A pergola or patio beam — check what the beam itself is fixed to, not just the beam.
- Fence palings, a gutter or a carport edge — not load-bearing anchors. This is the most common cause of a failed install.
Sails are supplied without hardware unless the product page says otherwise, so check before you order. Our 304 stainless steel fixing kits and tensioners are made for outdoor use and resist corrosion near a pool or the coast — worth specifying if you are anywhere with salt in the air.
Give it a pitch
Never install a sail flat. Set the corners at different heights so there is a fall across the fabric — a common approach is one corner noticeably lower than the others. A flat sail pools water, and a pool of water is heavy enough to stretch the fabric and pull on the anchors.
A pitch also looks better. A sail with a twist in it reads as designed; a flat one reads as a tarp.
A short checklist before you order
- Measured every side between fixing points, plus both diagonals
- Subtracted 30–40 cm per corner for hardware
- Chosen the shape your anchors actually allow
- Decided breathable or waterproof, honestly
- Confirmed every anchor can take load
- Planned a height difference between corners
- Added a fixing kit and tensioners if the sail does not include them
If you are unsure about a span or an anchor, send us the measurements before you order — we would rather check them with you than have a sail come back. Free delivery Australia-wide on every order.
