initially, calibrated SAR backscatter is scaled so that 1 represents a fully isotropic scatterer.
However, as most of the values range between 0. and 0.1, the data is translated into log-scale. You can to this by right-clicking the raster and selecting “Convert to/from dB”
Then you will have values ranging between -40 and +5 (roughly) as used in many studies.
Some more details on this: Classification Sentinel-1 problems with MaxVer