Harth / Free tools
Site & solar
Three tools for the site questions that shape a scheme before detailed design: how much floor area and footprint a site allows, where the sun is through the day and the year, and how long a shadow or a shading overhang will be at a given sun angle.
3 site & solar tools
Free export on every toolFloor area ratio & site coverage
Calculate FAR and footprint coverage separately against your own planning limits.
Interactive tool · Free exportSun-path diagram generator
Plot the sun for a selected day and both solstices; export SVG, PNG and hourly data.
Interactive tool · Free exportShadow length & overhang calculator
Explore ground shadows and wall shading from entered sun angles and orientation.
Interactive tool · Free exportAbout the site & solar tools
The floor area ratio calculator reports FAR and site coverage separately against the limits you enter, and shows the remaining floor area and footprint. The sun-path diagram generator plots solar altitude and azimuth for a chosen date and both solstices at any latitude and longitude, using the SunCalc library, and exports the diagram as SVG or PNG with hourly data as CSV. The shadow and overhang calculator turns a sun altitude, azimuth and facade orientation into ground shadow length and the depth of shade an overhang casts down a wall.
The FAR and shadow calculators default to imperial units with a metric switch. Sun position uses a fixed offset from UTC that you enter, so you can match standard or daylight-saving time for the selected date.
None of these tools looks up zoning rules or climate data; they calculate from the values you provide and state their assumptions on the page. Use the outputs as a starting point, then confirm limits with the planning authority and orientation on site.
Start with: Floor area ratio & site coverage, Sun-path diagram generator, Shadow length & overhang calculator.
Popular questions
How do you calculate floor area ratio?
Divide the building's gross floor area by the lot area. A 4,800 ft² building on a 6,000 ft² lot has a FAR of 4,800 ÷ 6,000 = 0.8.
From the Floor area ratio & site coverage
What is a sun path diagram?
A chart of the sun's positions across the sky for a place and date, plotted by altitude and azimuth. It shows where the sun rises and sets, how high it gets and which directions receive direct sun during the day.
From the Sun-path diagram generator
How do you calculate the length of a shadow?
Divide the object's height by the tangent of the sun's altitude. A 10 ft pole with the sun 30° above the horizon casts a shadow of 10 ÷ tan(30°), about 17.3 ft.
From the Shadow length & overhang calculator
What does a FAR of 1.0 mean?
The total floor area can equal the lot area. On a 10,000 ft² lot that is 10,000 ft², for example two stories of 5,000 ft² or four stories of 2,500 ft².
From the Floor area ratio & site coverage
How high is the sun at noon on the winter solstice?
In the northern hemisphere, about 90° minus your latitude minus 23.44°. At 40°N that is about 26.6°, and at 30°N about 36.6°.
From the Sun-path diagram generator
Other free tool categories
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Need the sun for a specific place? Browse the sun-path diagrams by city, each pre-set with its coordinates and time zone.
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