Roof star size for street view
Choose a lighted star for a roof peak or gable by how big it will look from the street. Enter the distance from the sidewalk to the house and the star’s height to compare its apparent size with the full moon — a handy yardstick for Prince William County lots with deep front setbacks.
sight line = √(distance² + height²); apparent size° = 2 × atan((diameter ÷ 2) ÷ sight line); moons = apparent ÷ 0.52°; size for target = 2 × sight line × tan(target × 0.52° ÷ 2)
When to use
Use this before you buy a 24-, 36-, or 48-in star. Sizing guides usually group stars by viewing distance; this turns that into geometry so you can see how much a star shrinks on a lot that sits far back from the road.
The full moon looks about 0.52° across. A star that looks one to three moon-widths across reads clearly from a car without overpowering the roofline.
The gable share line is a proportion check: a star much wider than about a quarter of the gable it sits on starts to look crowded.
Sidewalk or street edge to the front wall.
Roof peak height minus about 5 ft.
Tip to tip.
1–3 is a typical range.
Width of the roof face or gable behind the star.
Worked example
With the form defaults, here is the arithmetic the Calculate button runs:
Sight line = √(80² + 18²) = 82.00 ft.
Apparent size = 2 × atan(1.00 ÷ 82.00) = 1.40°, or 1.40 ÷ 0.52 = 2.7 moon widths.
For 2.0 moon widths: 2 × 82.00 × tan(0.52°) × 12 = 18 in. Gable share = 2.0 ÷ 24 = 8%.
Second example: one input changed
From the defaults (Distance from viewer to house (ft) = 80; Star height above viewer’s eyes (ft) = 18; Star diameter (in) = 24; Target apparent size (moon widths) = 2; Gable width at the star (ft) = 24), the calculator shows:
Sight line: 82.0 ft
Your 24 in star looks 1.40° across — about 2.7 moon widths
Diameter for 2.0 moon widths: 18 in
Share of gable width: 8%
Now change Distance from viewer to house (ft) from 80 to 140 and keep the other entries. The result becomes:
Sight line: 141.2 ft
Your 24 in star looks 0.81° across — about 1.6 moon widths
Diameter for 2.0 moon widths: 31 in
Share of gable width: 8%
Pushing the viewer back to 140 ft shrinks the same 24-in star to about 1.6 moon widths, and the size needed for a two-moon look climbs from about 18 in to about 31 in. On a deep lot, stepping up one star size does more than adding a second small star.
Limits / assumptions
Units: feet for distances, inches for the star, degrees for apparent size.
Assumptions: star faces the viewer; 0.52° is the average apparent width of the full moon.
Not modeled: brightness, bulb density, or glare — a dense LED star reads larger at night than its frame size.
Planning tips
- Stand where most people see the house — usually the street in front of the driveway — and measure from there, not from the porch.
- If you are torn between two sizes, tape a cardboard circle of each diameter to the gable in daylight and look from the street.
- A star on a garage gable closer to the street looks bigger than the same star on the main roof farther back; use separate distances for each spot.
Roof work is the riskiest part of decorating. Mount stars from a properly set ladder or a dormer window where possible, never on a wet or frosty roof, and secure them against wind.
FAQ
Why compare with the moon?
Everyone knows roughly how big the full moon looks, so it is an easy mental yardstick for apparent size.
What size do most front yards use?
Many homes use 24–36 in stars. Run your own distance: on a typical lot set back 50–80 ft, a 24-in star looks about two moon widths or more.
Does height matter much?
Only a little unless the star is very high and close. It mostly changes the sight line for tall two-story peaks near the sidewalk.
3-D or flat star?
A flat star works when people only see the house from the front; a 3-D star reads from several directions on corner lots.