I'm building an API where user can insert a number (3857, 27700,etc.) and my API will give the projected bounds. I'm using pyproj's

crs_number = 27700    
crs_custom = CRS.from_user_input(crs_number)

this function is giving me bounds but it is showing bounds like


instead of


How do I get the expected bounds?

  • The area_of_use.bounds are in WGS84 so that property is consistent across all CRSs, so just project them to your target if that's what you're looking for
    – mikewatt
    Mar 19, 2021 at 20:00
  • How can I project? Mar 19, 2021 at 20:00
  • There are examples in the docs: pyproj4.github.io/pyproj/stable/…
    – mikewatt
    Mar 19, 2021 at 20:40

1 Answer 1


Here is simple solution following the @mikewatt advise

from pyproj import CRS, Transformer

in_crs = CRS.from_epsg(4326)
out_crs = CRS.from_epsg(3857)
x_min, y_min, x_max, y_max = out_crs.area_of_use.bounds

Then project your bottom left corner and top right corner in the output crs :

proj = Transformer.from_crs(4326, 3857, always_xy=True)
bl = proj.transform(x_min, y_min)
tr = proj.transform(x_max, y_max)


Following this question I asked on github and thanks to @snowman you can use :

from pyproj import CRS, Transformer

crs = CRS("EPSG:3857")
transformer = Transformer.from_crs(crs.geodetic_crs, crs, always_xy=True)

you can find the issue and the PR on github.

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