RetractWise

Awning Shade Calculator (Sun Angle and Shade Depth)

By Retract Wise Editorial TeamUpdated Editorial standards

An awning's projection is not its shade. On a west-facing patio at 5 pm in August, a 10 ft awning may shade only 3 or 4 ft of the space where you sit. This calculator traces the sun's rays past your awning's front bar so you can see how much usable shade you get at the hours you actually spend outside.

Your location and time
Phoenix 33.4, Atlanta 33.7, Denver 39.7, Chicago 41.9, Seattle 47.6
Solar noon is when the sun is highest, often about 1 pm under daylight saving time
Your awning

Key takeaways

  • Shade depth depends on the sun's profile angle against your wall, not just its height in the sky.
  • West and east walls get low, raking sun when you most want shade. Extra projection helps less than a drop valance or side screen.
  • South walls are the easy case in summer: a modest projection shades deeply around midday because the sun is high.
  • Steeper pitch lowers the front bar, which slightly improves late-day shade but costs headroom and view.

How the calculation works

The calculator finds the sun's altitude and azimuth for your latitude, date and solar time using the standard declination and hour-angle equations (accurate to within about a degree, which is far finer than the variation between real installations). It then projects the sun onto a vertical plane perpendicular to your wall. That projection is the profile angle, the angle that matters for any horizontal overhang.

From the bracket height, projection and pitch, it locates the front bar: out from the wall by projection × cos(pitch) and down from the bracket by projection × sin(pitch). A ray through the front bar at the profile angle tells you where the shadow edge lands, at the ground and at whatever height you choose (seated head height is the useful one for a patio).

Worked example: Latitude 34°N, west wall, August 15, 5 pm solar time. The sun is about 20° up and almost square to the wall, so the profile angle is also about 20° (tan 20° ≈ 0.36). A 10 ft awning at 15° pitch, mounted at 9 ft, puts its front bar 9.7 ft out and 6.4 ft up. At seated head height (4 ft) the shade edge sits 9.7 − (6.4 − 4) / 0.36 ≈ 3.0 ft from the wall. On the ground there is no awning shade at all: the shadow of the front bar lands on the wall about 2.9 ft above the patio. Seven of the awning's ten feet are shading nothing you sit in.
Retract Wise analysis: run the same example with a 13 ft awning and seated shade jumps to about 8 ft. But look at why: at 15° the longer arms also drop the front bar to about 5 ft 8 in, below head height. Almost all the late-day gain from extra projection comes from lowering the shade edge, not from reaching further. A drop valance or front screen on a 10 ft awning lowers the shade edge the same way, keeps the frame at a comfortable height and can be rolled up when the sun moves. Test both options above before paying for the bigger frame.

Reading the results

  • Seated shade is the number to plan furniture around. If your table is 7 ft from the wall and seated shade is 5 ft, the far chairs are in sun.
  • Ground shade tells you how much of the deck or pavers stay cool, which matters for bare feet and for heat radiating back up.
  • Wall shadow line shows how much glass is shaded. If the line sits above your window sill, part of the window is still taking direct sun.
  • House shade means the sun is behind the wall: the awning is irrelevant at that hour.

Solar time versus clock time

The calculator uses solar time, where 12:00 is the moment the sun is highest. Clock time differs because of time zones and daylight saving. In most of the continental US under daylight saving time, solar noon falls between about 12:45 pm and 1:45 pm. Add roughly one hour to the solar time to get the clock time, then adjust for where you sit in your time zone (later in the west of a zone, earlier in the east).

Limitations

The model assumes a flat, level patio, a wall that runs straight, and an awning wider than the area you care about. It ignores side spill near the awning's ends, trees and neighboring buildings, and fabric translucency (light fabrics let some light through even in shade). For a full-season picture, see our precomputed shade coverage tables.

Frequently asked questions

How far should an awning project to shade a west-facing patio?

Plan on projection alone not being enough after about 4 pm in summer. A 10-12 ft projection plus a drop valance or vertical screen gives far better late-day coverage than a 14 ft projection on its own.

Does a steeper pitch give more shade?

Slightly, late in the day, because the front bar sits lower and blocks low sun earlier. Each extra 5° of pitch on a 10 ft awning drops the front bar by about 10 in, which costs headroom. The calculator lets you test the trade.

Why does my south-facing awning shade so much more in June than in September?

In June the midday sun is much higher, so the shadow falls almost straight down. By late September it is around 20° lower at most US latitudes, and the same awning casts a shallower shadow.

Is the calculator accurate enough to size an awning?

Yes for planning. The sun math is accurate to about a degree. The bigger uncertainties are your exact mounting height and pitch, so measure those carefully with the help of our measuring guide.

Can I use it for a window awning?

Yes. Set the bracket height to the top of the drop arm mounting, use the arm length as projection and the arm angle as pitch, then read the wall shadow line against your window sill height.