Awning brochures quote projection, but what you actually buy is shade, and the shade moves. We calculated where an awning's shadow falls using standard solar geometry (solar declination and hour angle) for 14 North American cities, three dates in the cooling season and several times of day. Every figure below is reproducible, and our shade calculator runs the same math for any location and awning size.

Method and assumptions

Sun position from the standard declination approximation (Cooper's equation) and hour angle. Times are local solar time: solar noon is when the sun is highest, typically between about 12:00 and 1:30 pm on daylight saving clocks in the US.
Reference patio awning: 10 ft (3.05 m) projection, front bar 7.5 ft (2.29 m) above the ground. Shade depth is measured from the wall outward, at right angles to the wall, assuming flat ground.
Window tables: the projection a horizontal awning needs so the shadow of its front edge reaches the sill, with the awning mounted 6 in (0.15 m) above the top of the window.
"Wall shade" means the sun is behind the wall, so the whole area is shaded by the building itself. "0 ft" means the shadow of the front bar falls on the wall side of the awning's footprint, so the ground directly in front of the wall is still in sun.
Geometry ignores side panels, valances, terrain, nearby trees and buildings. Real shade on a patio is a parallelogram that also shifts sideways when the sun is not square to the wall; the calculator reports that sideways shift.

Sun height at solar noon

The higher the sun, the closer to the wall the shadow falls, and the more of the awning's footprint is shaded. The noon sun is roughly 90° minus your latitude, plus the sun's declination (about +23.4° at the June solstice and 0° at the equinoxes).

Solar altitude at solar noon
City	Latitude	Jun 21	Aug 1	Sep 21
Miami, FL	25.8°	88°	82°	64°
Houston, TX	29.8°	84°	78°	60°
Phoenix, AZ	33.4°	80°	75°	56°
Los Angeles, CA	34.1°	79°	74°	56°
Nashville, TN	36.2°	77°	72°	54°
Washington, DC	38.9°	75°	69°	51°
Denver, CO	39.7°	74°	68°	50°
New York, NY	40.7°	73°	67°	49°
Chicago, IL	41.9°	72°	66°	48°
Boston, MA	42.4°	71°	66°	47°
Toronto, ON	43.7°	70°	64°	46°
Minneapolis, MN	45.0°	68°	63°	45°
Portland, OR	45.5°	68°	62°	44°
Seattle, WA	47.6°	66°	60°	42°

South-facing patio: shaded depth at solar noon

Shaded depth for the reference 10 ft awning with its front bar at 7.5 ft on a wall facing due south.

Depth of shade from the wall, 10 ft projection, south wall, solar noon
City	Jun 21	Aug 1	Sep 21
Miami, FL	9.7 ft	9.0 ft	6.3 ft
Houston, TX	9.2 ft	8.4 ft	5.7 ft
Phoenix, AZ	8.7 ft	7.9 ft	5.0 ft
Los Angeles, CA	8.6 ft	7.8 ft	4.9 ft
Nashville, TN	8.3 ft	7.5 ft	4.5 ft
Washington, DC	7.9 ft	7.1 ft	3.9 ft
Denver, CO	7.8 ft	7.0 ft	3.7 ft
New York, NY	7.7 ft	6.8 ft	3.5 ft
Chicago, IL	7.5 ft	6.7 ft	3.2 ft
Boston, MA	7.4 ft	6.6 ft	3.1 ft
Toronto, ON	7.2 ft	6.4 ft	2.8 ft
Minneapolis, MN	7.0 ft	6.2 ft	2.4 ft
Portland, OR	7.0 ft	6.1 ft	2.3 ft
Seattle, WA	6.6 ft	5.7 ft	1.7 ft

What it means: in June the shadow of the front bar sits only about 1 to 3 ft inside the awning's footprint in every city, so a 10 ft unit shades roughly 7 to 9 ft of patio. By the September equinox the same awning shades far less in Seattle or Minneapolis than in Miami. If you want late-season shade in the north, add projection or a valance, or lower the front bar with more pitch.

West-facing patio: the afternoon problem

Shaded depth for the same awning on a wall facing due west, on August 1, by solar time.

Depth of shade from the wall, 10 ft projection, west wall, August 1
City	2 pm	3 pm
Miami, FL	5.9 ft	3.2 ft
Houston, TX	5.9 ft	3.1 ft
Phoenix, AZ	5.8 ft	3.1 ft
Los Angeles, CA	5.8 ft	3.1 ft
Nashville, TN	5.8 ft	3.0 ft
Washington, DC	5.7 ft	3.0 ft
Denver, CO	5.7 ft	2.9 ft
New York, NY	5.7 ft	2.9 ft
Chicago, IL	5.6 ft	2.9 ft
Boston, MA	5.6 ft	2.8 ft
Toronto, ON	5.6 ft	2.8 ft
Minneapolis, MN	5.5 ft	2.7 ft
Portland, OR	5.5 ft	2.7 ft
Seattle, WA	5.4 ft	2.6 ft

What it means: on a west wall the shaded strip collapses quickly as the afternoon goes on, because the sun drops toward the horizon straight in front of the awning. By 5 or 6 pm the front bar's shadow falls back against the wall in every city. Adding projection barely helps; a drop shade or solar screen hanging from the front bar is the effective fix, which is why installers so often pair the two on west exposures.

South windows: projection needed for full shade at noon

Projection needed for a horizontal awning mounted 6 in above the window to shade the full window height at solar noon.

Required projection, south-facing window, solar noon
City	4 ft window, Jun 21	4 ft window, Sep 21	6 ft window, Jun 21	6 ft window, Sep 21
Miami, FL	0.2 ft	2.2 ft	0.3 ft	3.2 ft
Houston, TX	0.5 ft	2.6 ft	0.7 ft	3.8 ft
Phoenix, AZ	0.8 ft	3.0 ft	1.1 ft	4.3 ft
Los Angeles, CA	0.8 ft	3.1 ft	1.2 ft	4.4 ft
Nashville, TN	1.0 ft	3.3 ft	1.5 ft	4.8 ft
Washington, DC	1.2 ft	3.7 ft	1.8 ft	5.3 ft
Denver, CO	1.3 ft	3.8 ft	1.9 ft	5.4 ft
New York, NY	1.4 ft	3.9 ft	2.0 ft	5.6 ft
Chicago, IL	1.5 ft	4.1 ft	2.2 ft	5.9 ft
Boston, MA	1.5 ft	4.1 ft	2.2 ft	6.0 ft
Toronto, ON	1.7 ft	4.3 ft	2.4 ft	6.3 ft
Minneapolis, MN	1.8 ft	4.5 ft	2.6 ft	6.5 ft
Portland, OR	1.8 ft	4.6 ft	2.6 ft	6.7 ft
Seattle, WA	2.0 ft	5.0 ft	2.9 ft	7.2 ft

What it means: the common rule that a south window awning should project roughly half to two thirds of the window height is generous for midsummer but close to the mark for the equinox, when cooling loads are still significant in much of the US. Window awnings are usually sloped and have side panels or valances, which shade more than this horizontal model.

West windows: why depth alone fails

Projection needed for full shade of a 4 ft west-facing window on August 1.

Required projection, west-facing 4 ft window, August 1
City	2 pm	3 pm	4 pm
Miami, FL	2.4 ft	4.1 ft	6.6 ft
Houston, TX	2.5 ft	4.1 ft	6.6 ft
Phoenix, AZ	2.5 ft	4.1 ft	6.5 ft
Los Angeles, CA	2.5 ft	4.2 ft	6.5 ft
Nashville, TN	2.5 ft	4.2 ft	6.6 ft
Washington, DC	2.6 ft	4.2 ft	6.6 ft
Denver, CO	2.6 ft	4.2 ft	6.6 ft
New York, NY	2.6 ft	4.3 ft	6.6 ft
Chicago, IL	2.6 ft	4.3 ft	6.6 ft
Boston, MA	2.6 ft	4.3 ft	6.6 ft
Toronto, ON	2.6 ft	4.3 ft	6.7 ft
Minneapolis, MN	2.7 ft	4.4 ft	6.7 ft
Portland, OR	2.7 ft	4.4 ft	6.7 ft
Seattle, WA	2.7 ft	4.4 ft	6.8 ft

What it means: by mid afternoon a west window would need an impractically deep horizontal awning. Steeply pitched window awnings with closed sides, vertical exterior screens, or drop-arm awnings that angle down toward the glass are the practical answers. This is consistent with the U.S. Department of Energy's finding that awnings cut solar heat gain more on west-facing windows (up to 77%) than south-facing ones (up to 65%): west glass gets more of the afternoon load, so shading it pays off more, but only with a design that blocks low sun.

Practical takeaways

South walls: a standard retractable projection (8 to 12 ft) gives good midday shade through summer across the US. Extra projection mainly helps in spring and autumn.
West and east walls: plan for vertical shade (drop shades, side screens or valances) rather than buying the deepest awning available.
Lowering the front bar with more pitch moves shade outward. Check headroom: most people want the front bar at 7 ft or higher. See projection and pitch.
Northern latitudes lose shade fastest as the season advances; southern cities keep a high sun longer.

Citing this data

You are welcome to cite these tables with a link to this page. The underlying formulas are standard and documented in the method section above, so anyone can reproduce or extend them.

Sources and further reading

U.S. Department of Energy, Energy Saver: Energy Efficient Window Attachments
Cooper, P. I. (1969), "The absorption of radiation in solar stills", Solar Energy 12(3): source of the declination approximation.
Duffie, J. A. and Beckman, W. A., Solar Engineering of Thermal Processes (Wiley): standard reference for solar angle formulas.
NOAA Global Monitoring Laboratory: Solar Calculation Details.