Equivalent focal length

Any lens on a crop sensor camera will give equivalent field of view as lens focal length times crop factor on a full frame camera. For e.g. 50mm lens on an APS-C with 1.6x crop factor sensor is equivalent to 80mm on full frame.
50mm lens on full frame approximates FoV of the human eye, that is around 47 degrees.
50mm on an APS-C has FoV of 30 degrees.
50mm on APS-C is equivalent to 80mm on full frame (30 degrees FoV)
50mm on full frame is equivalent to 30mm on APS-C (47 degrees FoV)