Space simulation tool
Window Sunlight and Indoor Sun-Reach Calculator
The window calculator links an outdoor sun position to a simple cutaway room. It estimates whether the sun faces the window and, when it does, how far the direct-light patch can travel across the floor.
- Cost
- Free
- Account
- Not required
- Project data
- Browser-local
Sun angle 38.3° · direct sun now · Drag the compass or timeline to update
What this tool calculates
- Whether the sun is in front of or behind the window plane
- Approximate floor penetration from solar altitude and window geometry
- Lateral movement caused by an oblique solar direction
- Blocking from the outdoor obstacles already drawn on the map
How to use it
- 01
Aim the window
Rotate the compass toward the direction the window faces, not the direction you face while looking outside.
- 02
Enter its dimensions
Measure clear glazed width, height and the sill’s height above the floor.
- 03
Add the outside context
Return to Outdoor map and add the buildings, walls or trees that cross the window’s view of the sky.
How to read the result
Sun reach
This is the estimated perpendicular distance of direct light across a level floor. It is not the overall brightness of the room.
No direct sun
A zero can mean night, the sun is behind the window, or a modeled obstacle blocks the solar ray.
Limits you should know
- Glass coatings, curtains, deep reveals and roof overhangs are not yet modeled.
- Diffuse daylight and reflected light can brighten a room even when direct sun reach is zero.
- Measurements assume a level floor and a vertical window plane.
Questions about this calculator
Does a north-facing window always get no sun?
No. The answer depends on hemisphere, season, latitude and obstructions. Near the tropics, the sun can pass north or south of a location during different months.
Is sun reach the same as daylight?
No. Sun reach tracks the direct beam. Daylight also includes diffuse sky light and reflections from surrounding surfaces.
Methodology version 1.1 · Reviewed August 8, 2026