Awning Size Calculator

Why the shade is shallower than the awning

Sunlight comes in under the front edge. With the sun at an angle a above the ground straight out in front of the wall, a ray that just grazes the front bar at height h reaches the ground h / tan a inside it, so an awning that projects p shades the ground out to p − h / tan a from the wall. The higher the front edge and the lower the sun, the more of the patio the sun gets back.

A worked case, the one the calculator is tested on: a south-facing wall in London at 13:00 BST on 21 June, when the sun is 61.9° up and almost due south (NOAA's equations put it at an azimuth of 178.9°). An awning projecting 2.5 m (8 ft 2 in) with its front at 2.4 m (7 ft 10 in) shades 2.5 − 2.4 / tan 61.9° = 1.22 m (4 ft) of patio. At the same hour on 31 August the sun is 47° up and the same awning shades only 0.27 m (10 in). That is why the calculator looks at the month ends as well as the solstice: the end of the season, not midsummer, is the hard case.

The profile angle: the sun as the awning sees it

The sun is seldom straight out in front of the wall. What matters for an awning is the angle the sun's rays make in a slice cut straight out through the wall, the profile angle (also called the vertical shadow angle). With the sun at altitude a and an angle r round from straight out, tan(profile) = tan a / cos r. Sun coming in from the side has a steeper profile angle than its altitude, so it is easier for the awning to keep it off the ground near the wall, though it then slips in at the open ends instead (the side spill below). When r passes 90° the sun is behind the wall and the house shades the patio itself.

How the calculator sizes it

For the place you pick it follows the sun every quarter hour through your hours, on the summer solstice and the last day of each summer month (May to August north of the equator, November to February south of it), or through the whole year. The quarter hour with the lowest profile angle, with the sun in front of the wall, is the worst moment; the arms that keep the shade as deep as you asked at that moment keep it at least that deep at every other one.

The front bar is set at the head room you give (2.1 m or 7 ft to start with, a little over markilux's own guide of about 2 meters) and the pitch follows from the height on the wall: the awning slopes from its fixing down to that bar. The pitch is held to 5°–35°, the range markilux's 990 and 6000 cassettes are made to; weinor's models adjust from 5° to 40° or 45°. markilux suggests planning on about 15°, and its awning covers only rinse themselves clean in the rain at 14° or more, so the calculator tells you when the slope comes out flatter than that and how high the fixing would have to be for 14°. A fixed awning is built to whatever pitch you order, so the same reasoning holds.

Model	Largest width × projection	Pitch	Source
markilux 990	5 × 3 m (16 ft 5 in × 9 ft 10 in)	5°–35°	markilux
markilux 6000	7 × 4 m (23 ft × 13 ft 1 in)	5°–35°, or 36°–70°	markilux
markilux MX-1	7 × 4.15 m (23 ft × 13 ft 7 in)		markilux brochure
weinor Cassita II	5.5 × 3 m (18 ft 1 in × 9 ft 10 in)	5°–45°	weinor
weinor Semina	7 × 3.5 m (23 ft × 11 ft 6 in)	5°–40°	weinor
weinor Kubata	6.5 × 4 m, or 7 × 3 m	5°–40°	weinor

What sizes are sold

SunSetter, the big American maker, sells fixed sizes, and its projection goes with the width. On its Motorized model the 8 ft wide awning extends 7 ft, the 10 and 11 ft ones 9 ft and the 12 to 20 ft ones 10 ft 1 in; its XL models, 14 to 20 ft wide, extend 11 ft 8 in or 13 ft 1 in, and it asks for a mounting height of at least 7 ft 6 in (SunSetter Motorized, SunSetter Motorized XL). So a need for 9 ft 2 in of projection is, from SunSetter, the 10 ft 1 in model and at least 12 ft wide; the calculator picks that for you.

The European makers build to order up to each model's largest size, in the table above; weinor's dealers plan "the projection depth and width" to the patio (weinor). The largest projection on a folding-arm awning from either is about 4 m: markilux's MX-1 reaches 4.15 m, and weinor's largest, among them the Kubata, Opal Design II and Topas II, reach 4 m. For a sense of what people buy, the UK installer Samson Awnings says the most common size of higher-end retractable awning it sells is 4 m wide with a 3 m projection, made to measure in width (Samson Awnings). When the answer is more than any of these, the calculator says so and works out the drop screen that would do the job instead.

Low sun: drop fronts and side screens

Some walls are hard. Take a west-facing wall in Phoenix at 18:00 on 21 June: the sun is 18.7° up and nearly straight out from the wall, a profile angle of 19.4°. Keeping 10 ft (3.05 m) of patio shaded with the front bar at 7 ft (2.13 m) would take 28 ft 7 in (8.71 m) of arm, more than twice the longest awning sold. Even SunSetter's 13 ft 1 in XL, fitted at 9 ft, shades nothing at that hour. A screen hanging from the front bar is the answer: lowered 5 ft (1.52 m), the most SunSetter's drop screens go to (SunSetter Pro), the same awning keeps 7 ft 3 in (2.21 m) in shade. weinor's VarioShade valance drops up to 2.1 m (6 ft 11 in) from the front of its cassettes. Pick "Drop front" in the calculator and give the drop to see what it does.

Late and early in the day the sun also comes in from the side, and the shadow of the awning slides along the wall. The calculator works out how far, at the foot of the wall, and adds it to the width on each side. When it comes to more than 1 m (3 ft) on a side it suggests a side screen there instead; that cut-off is this calculator's own rule of thumb, because past it the extra width of awning mostly shades the lawn. How the sun moves across your garden goes into why the evening sun swings so far round.

The winter sun

A fixed awning stays out all year, and that is no bad thing on a south-facing wall: the low winter sun gets under it. In London at solar noon on 21 December (11:59 GMT) the sun is 15.1° up; under the same 2.5 m (8 ft 2 in) awning with its front at 2.4 m (7 ft 10 in) it lights the whole patio and the wall up to 1.72 m (5 ft 8 in), so a door or window below that gets the sun's warmth through the winter. The calculator shows this for your wall and your awning, and draws the winter ray in the section when you pick a fixed awning. A retractable awning rolled in lets all of it in. The choice between the two is in retractable vs fixed awnings, and what each kind costs in the types of awnings and what they cost.

Reading the result

• Projection is the length of the arms, the figure makers quote. The calculator compares it with the sizes sold; because the arms slope, the front stands out from the wall a little less ("reaches out").
• The table gives the shade depth for every hour on each date with the awning you are checking, against the depth you asked for. Change "Check an awning that projects" to see what a smaller, cheaper size would give, and tap any cell to draw that moment.
• Hours are your clock's, summer time included, at the place you pick.

If a wall is hopeless for an awning, a sail or a pergola can be put where the sun is rather than where the wall is: shade sail vs awning vs pergola compares them, the best shade for a south-facing garden and shade for hot climates go further, and an awning over a window also cuts the heat indoors (shading windows to cut cooling costs). Once it is up, how to clean an awning keeps the cover going.

Sources: the sun's position from NOAA's solar calculator equations (NOAA Global Monitoring Laboratory); sizes and pitch ranges from SunSetter, markilux (its 2 m head room and 15° guide, on that page; 14° for its covers to clean themselves, in its patio and balcony awnings brochure), weinor and Samson Awnings, as linked above, read October 2026. Makers change their ranges; check the size with your dealer before you order.