The solar flux unit (sfu) is a non-SI unit of spectral flux density often used in solar radio observations, such as the F10.7 solar activity index. It is equivalent to 10<sup>−22</sup> watts per square metre per hertz (SI), 10<sup>−19</sup> ergs per second per square centimetre per hertz (CGS), and 10<sup>4</sup> Jansky.