Spatial Reference System Functions

ST_Transform

To SRID variant

Description: Returns a new geometry with its coordinates transformed to a different spatial reference system
Input Argument #1: Geometry (WKB)
Input Argument #2: Target CRS SRID (Integer) Output: Geomery (WKB)

SELECT ST_AsText(
  ST_Transform(
    ST_GeomFromText(
      'POLYGON((743238 2967416,743238 2967450,743265 2967450,743265.625 2967416,743238 2967416))',
      2249
    ),
    4326
  )
) AS wgs84_geom;

Result

POLYGON ((-71.1776848522251 42.39028965129019, -71.17768437663263 42.390382947800894, -71.17758443054647 42.39038266779173, -71.17758259272306 42.39028936479872, -71.1776848522251 42.39028965129019))

Note #1
PostGIS overloaded variants supporting direct PROJ 4 string injection are not (yet) implemented

Note #2
Supported SRIDs are defined in LocationTech's PROJ4 binding

Note #3
Be sure input geometries, whether serialized from text WKT or WKB, are loaded with the proper SRID definition.
That is a prerequisite in order for this function to operate properly, as the source SRID is used to compute the proper transformation

To PROJ4 string variant

From PROJ4 string to SRID variant