Awning Size Calculator
Enter the window's width, the drop from where the awning meets the wall down to the sill, and your latitude. The calculator gives the projection and width that keep the summer noon sun off the glass.
- Projection from latitude
- Summer shade
- Winter sun
This is for a window facing the equator: south in the northern hemisphere, north in the southern.
An awning works because the sun is high in summer and low in winter. At latitude 40°, the summer noon sun is about 73° high. An awning sticking out about a third of the drop to the sill shades the whole window, but the low winter sun still reaches in.
Awning projection chart
5 ft drop to the sill. Search for a latitude.
| Latitude | Summer sun | Projection (ft) | City example |
|---|---|---|---|
| 10 | 90° | 0 | Panama |
| 25 | 88° | 0.14 | Miami |
| 33 | 80° | 0.85 | Los Angeles |
| 40 | 73° | 1.49 | New York |
| 51 | 62° | 2.61 | London |
| 60 | 53° | 3.71 | Oslo |
Projection to shade the window fully at summer noon.
Latitude and projection
5 ft drop. Slide the latitude.
The dashed line is the summer noon sun just touching the sill.
How to size an awning
Sun angle first. Step through it.
Latitude
Your location.
Morning and evening sun on east and west windows is low. Use blinds or vertical screens there instead.
Fixed, retractable or louvred
Awning types. Compare them.
Permanent frame.
Rolls away.
Angled slats.
Retractable awnings must be wound in during strong wind.
Before fitting
Awning checks. Tick each item.
Tick each item as you go.
Fix awnings into solid masonry or framing, not just the cladding.
What you get
Awning sizing. Each tile explains one result.
Out from the wall.
Past the frame.
Height at noon.
Lower, gets in.
Share of window.
Shading glass from outside stops far more heat than blinds inside the window.
Frequently Asked Questions
No question matches that search.
How far should an awning stick out?
Far enough to shade the window at summer noon: the drop to the sill divided by the tangent of the sun's height.
How wide should an awning be?
About 6 inches, or 15 cm, wider than the window on each side.
Does an awning block winter sun?
A well sized one lets most of the low winter sun in.
What angle is the summer sun?
At noon on the longest day, about 90° minus your latitude plus 23.4°.
Do awnings work on east windows?
Not well. The morning sun is low and gets under them.
Do awnings cut cooling costs?
Yes. Shading the glass outside stops much of the heat before it gets in.
How much slope should an awning have?
At least about 15° so rain runs off.
Shade in summer, sun in winter
Size the awning from your latitude and window, so the high summer sun is blocked and the low winter sun still warms the room.
More size calculators
Each one has its own calculator, worked examples and answers to common questions.