A sunspot's typical maximum magnetic field strength is about 4,000 gauss. The strongest fields are concentrated in the dark central umbra, where magnetic pressure suppresses convection and lowers the temperature compared with the surrounding photosphere.
Sunspot fields commonly range from roughly 1,000 to 4,000 gauss, with larger and more complex spots generally supporting stronger fields. For comparison, Earth's surface magnetic field is less than 1 gauss, so a powerful sunspot can have a field thousands of times stronger than the planet's ambient field.
The field is measured through magnetism's effect on spectral lines, especially Zeeman splitting. Oppositely polarized regions often appear in pairs or groups, reflecting the magnetic structure of the solar dynamo. When these fields become twisted or stressed, they can reconnect and release energy as solar flares and coronal mass ejections.
The figure is a typical upper value, not a universal limit: exceptional observations have recorded fields above 4,000 gauss in rare solar regions.