GPS Coordinates Question

[tanjiajun_34]

Hi! I am no good in programming so please excuse if I am saying anything stupid.

So yeah I am working on an Android application that allows the user to enter a location's lat and long coordinates and using the coordinates, it will search a database (Google firebase actually) containing many different location's coordinates and will return those locations that are of a certain radius.

 

My first idea was to "rip" all the locations in the database to the application and calculating all the coordinates' distance from the user entered coordinates one by one with the coordinates that the user entered. However, this is of course pretty resource demanding if the database gets large.

 

So I am asking, if given a lat and long coordinate and the radius, is there a formula or what to get the range of lat and long numbers that will fall inside the radius?