How to Measure for a Retractable Awning (Without Ending Up With Low Headroom)
To measure for a retractable awning, record three numbers: the clear wall width available for the mounting brackets, the projection (how far out the awning should reach), and the highest solid mounting height. Then check that the front bar will still clear about 7 ft (2.1 m) at your chosen pitch. That last check is the one most people skip, and it is why awnings end up too low to walk under.
Key takeaways
- Order width is set by the space you can actually bolt to, not the patio size. Allow 6-12 in (15-30 cm) beyond the area you want shaded on each side if the wall allows.
- For lateral arm awnings, width should normally be at least the projection plus about a foot, or the arms will not fold without crossing.
- Front bar height = mounting height minus projection x sin(pitch), minus valance drop. Aim for 7 ft (2.1 m) or more at the front.
- Find structure first. A mounting height that lands on siding over hollow sheathing is not a mounting height.
- Measure obstructions: doors that swing out, lights, gutters, downspouts, hose bibs, window trim, and roofline changes.
What you need
- 25 ft (7.5 m) tape measure, ideally with metric markings
- 4 ft (1.2 m) level or a laser level
- Stud finder, plus a small drill bit to confirm what is behind the cladding
- Ladder and a helper
- Phone for photos of every wall section, corner and obstruction
- A sketch of the wall elevation (front view) and a plan view (top-down)
Step by step: measuring the wall and patio
- Decide what you want shaded. Mark the area on the patio with chalk or tape: the table, the seating, the glass doors. Shade falls at an angle, so the patio area is a starting point, not the final width. The shade calculator shows where shade lands by time of day.
- Measure the clear mounting width. At the height you plan to mount, measure from the first obstruction on the left to the first on the right: corners, downspouts, windows that would be partly covered, light fixtures, vents. This is the maximum awning width (outside of the end caps or cassette).
- Find the maximum mounting height. Measure from the patio surface to the underside of the soffit or eave, or to the highest structural point (a header, rim joist or masonry course). Subtract the cassette or hood height, typically 8-12 in (20-30 cm), plus a few inches of working room for the bracket bolts.
- Locate structure along that line. Mark studs, the rim joist or header, and masonry type. Bracket positions follow structure, not the other way around. See awning mounting options for what each substrate needs.
- Measure available projection. From the wall outward, measure to anything that would block the extended awning: trees, a fence, a pool edge, a property line setback. Projection is measured horizontally from the wall to the front bar when the arms are fully extended at zero pitch; at real pitch the horizontal reach is a little less.
- Measure slope of the patio. Patios are pitched away from the house for drainage, often by 1/8-1/4 in per foot (1-2 percent). Measure headroom at the far edge, where the front bar will be, not at the wall.
- Record obstructions in the swing zone. Outward swinging doors, wall lights, cameras, gutters, satellite dishes and the arms' path as they fold back to the wall.
- Photograph everything. Include a tape measure in the shot. Installers and suppliers can spot problems from photos that a list of numbers hides.
Check front bar headroom at your pitch
An awning slopes down from the wall. The front bar drops by the projection multiplied by the sine of the pitch angle. Add the valance, which hangs below the front bar by 6-10 in (15-25 cm) on most models.
| Projection | 10 degrees | 15 degrees | 20 degrees | 25 degrees |
|---|---|---|---|---|
| 8 ft (2.4 m) | 1.4 ft (0.42 m) | 2.1 ft (0.63 m) | 2.7 ft (0.83 m) | 3.4 ft (1.03 m) |
| 10 ft (3.0 m) | 1.7 ft (0.53 m) | 2.6 ft (0.79 m) | 3.4 ft (1.04 m) | 4.2 ft (1.29 m) |
| 11.5 ft (3.5 m) | 2.0 ft (0.61 m) | 3.0 ft (0.91 m) | 3.9 ft (1.20 m) | 4.9 ft (1.48 m) |
| 13 ft (4.0 m) | 2.3 ft (0.69 m) | 3.4 ft (1.04 m) | 4.4 ft (1.37 m) | 5.5 ft (1.69 m) |
More on choosing the angle in awning pitch explained.
Width and projection rules that limit your order
Width vs projection on lateral arm awnings
Lateral arms fold flat against the roller when closed. Each arm is roughly as long as the projection, so two arms need room to fold side by side. As a rule, the width must exceed the projection by about 12-16 in (30-40 cm), depending on the arm design. Narrower awnings can sometimes use crossed (overlapping) arms mounted at different heights, at extra cost. If your wall is 9 ft wide but you want 10 ft of projection, a lateral arm awning may not be the right product at all.
Common size steps
Many manufacturers build to any width within a range, in 1 in or 1 cm steps, but sell projection in fixed steps tied to arm lengths, commonly 6.5, 8, 10, 11.5 and 13 ft (2.0, 2.5, 3.0, 3.5 and 4.0 m). Measure your ideal projection, then round down to the nearest available arm length unless the next size up still fits.
Matching width to the shade you want
Shade shifts sideways as the sun moves. A west-facing patio in late afternoon needs extra width on the south side to keep the table covered as the shadow slides. Adding a foot of width is usually cheap; adding projection is expensive and costs headroom. The awning size calculator and the shade coverage tables help turn this into numbers.
Obstruction checklist
- Door and window trim: brackets need flat contact, so trim may need notching or a mounting board.
- Gutters and fascia: a soffit or roof mount may be needed if the wall is too short below the eave.
- Outward-swinging doors and storm doors: check they clear the closed cassette and the brackets.
- Wall lights, cameras and doorbells: relocate or plan around them before installation day.
- Hose bibs, dryer vents and meters: brackets cannot sit over them, and vents should not blow into a closed awning.
- Roofline changes, bump-outs and chimney chases: they break the straight mounting line.
- Electrical: note where power for a motor can come from (see motors and controls).
What to send a supplier or installer
A complete measurement package avoids a second site visit and reduces the risk of a wrong order:
- Maximum mounting width and the reason for each end limit
- Mounting height, soffit height, and the patio-to-front-bar headroom target
- Desired projection and the maximum possible projection
- Wall construction and cladding (wood frame with siding, brick veneer, solid masonry, block, stucco)
- Orientation (which way the wall faces) and typical wind exposure
- Photos of the whole wall, each end, the soffit and any obstruction
If an installer will measure for you, see questions to ask an awning installer. If you are doing it yourself, the next step is how to install a retractable awning.
Frequently asked questions
Is awning width measured including the brackets?
Most manufacturers quote the overall width across the end caps or cassette. Brackets sit inside that width. Check the spec sheet, because some open awnings quote fabric width, which is a few inches narrower than overall width.
How high should a retractable awning be mounted?
High enough that the lowest point of the front bar or valance is at least about 7 ft (2.1 m) above the patio at your chosen pitch. In practice that usually means mounting at 8.5-10 ft (2.6-3.0 m), and higher for deep projections.
Can an awning be wider than my patio?
Yes, and it often should be. A slightly wider awning keeps shade on the patio as the sun moves, provided the wall has space and structure for the brackets.
What if my wall is not level?
Mount the awning level, not parallel to the siding lines. Small differences are taken up with shims behind brackets; larger ones need a continuous mounting board or spacers designed for the bracket.
How much projection do I need to shade a patio table?
It depends on the sun angle and orientation. At midday in summer a high sun casts shade close to the wall, while morning and afternoon sun pushes shade outward. Use the shade calculator with your latitude and orientation rather than a single rule of thumb.
Should I measure in inches or centimeters?
Use whichever the manufacturer orders in, and record both if you are unsure. Many European-made awnings are built in metric steps, so a metric measurement avoids rounding errors.
Sources and standards consulted
- EN 13561:2015, External blinds and awnings: performance requirements including safety (CEN)
- Somfy and other tubular motor installation and programming guides (manufacturer documentation)
- Manufacturer installation manuals for lateral arm, drop arm and cassette awnings (manufacturer documentation)
- International Residential Code (IRC), structural attachment and fastening provisions (ICC)
See how we research for our sourcing and verification process.