How big is a sunspot? The average sunspot is about the size of the entire planet Earth! However, sunspots come in a variety of sizes ranging from hundreds to tens of thousands of miles across (many times larger that Earth). Scientists measure the total size (area) of all of the sunspots seen on the sun every day to get a measure of how active the sun is. Sunspots are not permanent. They appear and disappear on the surface of the sun.