As a single star, the mass of Arcturus cannot be measured directly, but models suggest it is slightly larger than that of the Sun. Evolutionary matching to the observed physical parameters gives a mass of , while the oxygen isotope ratio for a first dredge-up star gives a mass of . The star displays magnetic activity that is heating the coronal structures, and it undergoes a solar-type magnetic cycle with a duration that is probably less than 14 years. A weak magnetic field has been detected in the photosphere with a strength of around half a gauss. The magnetic activity appears to lie along four latitudes and is rotationally-modulated.