Shadow Calculator
Enter a measured obstacle height to calculate shadow length and bearing. Place a simplified screen to compare local shade across dates.
Solar times, the sky view and date controls remain available.
Light on this day
Europe/Lisbon · Select any event to move the map to that instant. Times are displayed to the minute; selection keeps the calculated instant.
Sunrise and sunset use an open horizon and atmospheric refraction. Dawn/dusk use the sun’s center at −6°, −12° and −18°. Golden light uses −4° to +6°: a planning convention, not a weather forecast. Calculation notes →
Turn a height into a shadow.
A vertical height, level ground and the selected sun position. Add a measured obstacle to place its shadow on the map.
Direction is opposite the sun. Ground shadows lengthen rapidly near the horizon. Below 0° geometric elevation, this model draws no direct shadow.
A different season. A different light.
Keep your place and jump through the year.
Find your alignment.
Choose what you want to see from Lisbon, Portugal.
1 Choose your target
The pin is where you stand. Mark the landmark or direction you want the sun to line up with.
2 Choose the light
Set precise angles and tolerance
3 Pick your date range
Select a map target first, or open precise angles to enter a direction.
The target sets a compass direction, not the height of a landmark. Windows show when the Sun’s center is within the selected angular tolerance. Terrain, buildings and weather are not included in this alignment search. Near-horizon geometry is not a guarantee of a visible sunrise.
Shadow Length and Direction Calculator
A 10 m object casts a very different shadow at 10° and 30° solar elevation. Enter its height, then place and size an optional vertical screen to test whether its shade reaches your selected outdoor point.
Use this when: Use this when the primary question is an obstacle shadow: where it falls, how long it is and when it crosses an outdoor area.
Inputs this tool uses
- A receiving point and a date with local time and IANA time zone.
- Obstacle height and width in metres; position and rotation define an opaque vertical screen. Rotation is its normal measured clockwise from true north.
- Known or deliberately estimated dimensions, recorded separately from map appearance. Building and Tree labels do not add roof or canopy geometry.
What this tool calculates
- Uncapped geometric shadow length for a positive solar-center altitude
- Shadow bearing opposite the solar azimuth
- Screen-based blocking at the receiving point
- A map projection clipped at 100 km for display
How the estimate is made
The level-ground formula is height / tan(solar altitude), directed opposite solar azimuth. The numeric length is uncapped; the visual map vector is clipped at 100 km. Point blocking intersects a ray with a finite opaque vertical screen. A zero-opacity imported obstacle is ignored; positive opacity does not model partial transmission.
How to use it
- 01
Place the receiving point
Mark the patio, garden or outdoor area whose shade matters.
- 02
Add the obstruction
Choose Building, Wall or Tree and click its location. Add the best height and width you can verify.
- 03
Test critical times
Check morning, midday and afternoon on dates near both solstices before drawing a conclusion.
Worked example
For a 10 m obstacle with the sun at 30° altitude, the geometric length is 10 / tan(30°) = 17.3 m. At 10° altitude it is 56.7 m, so the same obstacle reaches much farther in the morning or winter. When the sun is at or below the horizon, SunCarta returns a zero-length shadow vector and does not draw a sunlit shadow.
How to read the result
Length versus display
A clipped ray is a visual limit, not the physical end of a shadow. The formula assumes a level plane and ignores Earth curvature at extreme lengths.
Buildings and trees
Both use an opaque vertical screen. Tree labels do not simulate foliage density, roof shapes or a volumetric building.
What to do next
Place the point where shade matters, add the nearest measured obstacle, then check morning, solar-noon and afternoon times near the dates that matter. If the result changes when you vary an uncertain height, measure that obstacle before relying on the comparison.
Limits you should know
- No automatic height or terrain dataset is loaded. Measure height relative to the receiving level.
- Screens omit depth, overhangs, roof shape, gaps and seasonal tree transmission.
- This is a planning comparison, not a professional survey or legal solar-access determination.
Questions about this calculator
What is the shadow-length formula?
For positive solar altitude, length = height / tan(altitude). Numeric length is uncapped; map display clips at 100 km. At or below the geometric horizon there is no sunlit shadow.
What does Rotation mean?
It sets the normal of the vertical screen clockwise from true north. It does not rotate a full three-dimensional building model.
Methodology version 2.0 · Reviewed September 18, 2026