c# - How to find other locations by given distance and coordinate in Google Maps -

i have many locations in google maps. , in database(sql server) stored coordinates. model this:

public class marker {    public int id { get; set; }    public string lat { get; set; }    public string long { get; set; } } 

1 coordinate(latitude , longitude) , 1 radius (i.e 100 meter) given me, should find locations in area inside radius locations list.

how can calculate distance radius on coordinates?

i think need use haversine formula foreach point given point , compare result radius.