mph vs miles per hour

mph and miles per hour both are nouns.

Word	Noun	Adjective	Verb	Adverb
mph	Yes	No	No	No
miles per hour	Yes	No	No	No

As nouns, mph and miles per hour are synonyms defined as:

mph and miles per hour: a speedometer reading for the momentary rate of travel

As nouns, mph and miles per hour are synonyms defined as:

mph and miles per hour: the ratio of the distance traveled (in miles) to the time spent traveling (in hours)

mph (noun)	miles per hour (noun)
a speedometer reading for the momentary rate of travel	a speedometer reading for the momentary rate of travel
the ratio of the distance traveled (in miles) to the time spent traveling (in hours)	the ratio of the distance traveled (in miles) to the time spent traveling (in hours)