It worth to take a look firstly at Acquisition resolution Level-1 SLC,
Source : https://sentinel.esa.int/web/sentinel/user-guides/sentinel-1-sar/resolutions/level-1-single-look-complex
Then
The spatial resolution of GRD products ,
Source : https://sentinel.esa.int/web/sentinel/user-guides/sentinel-1-sar/resolutions/level-1-ground-range-detected
