TERPS or ICAO Doc 8168 Vol 2 specify 200 ft/nm or 3.3% on a random route departure (TERPS terminology) or omnidirectional departure (ICAO Doc 8168 terminology) up to the first minimum instrument altitude. States may file exceptions, but I think rarely do so for this issue. But, the UK does use 500 feet for the end of Zone I instead of the standard 400 feet or 120 meters.
So all hills and mountains are levelled around airports until they meet a 3.3% gradient then!
