Work out satellite coverage area instantly with clear inputs, formula shown and shareable results.
A satellite's footprint is a spherical cap whose extent depends on altitude and the minimum usable elevation angle. At 550 km with a 25 degree mask the central angle is 13.4 degrees, giving a ground radius of about 1490 km and 6.8 million square kilometres - roughly 1.4% of Earth's surface, which is why megaconstellations need thousands of satellites.
Nadir angle
eta = arcsin((Re / Rs) cos(elevation))
Central angle and cap area
lambda = 90 - elevation - eta; area = 2 pi Re^2 (1 - cos lambda)
Because low angles mean long atmospheric paths, multipath and terrain blocking. Typical masks are 10-25 degrees for reliable links.
It depends on altitude: three at geostationary height, but hundreds to thousands in low Earth orbit.