Tile dimensions in degrees

I need to know for a given zoom level, the tile dimensions in degrees.
I assume every tile has the same dimensions.

E.g., if I have zoom level 2 where there are 4 x 4 tiles of 256 x 256
pixels each tile.

What is the tile dimensions (width and height of the tile) in degrees
or how to calculate the tile dimensions ?

I assume the following:

tile width in degrees = 360 / (4 x 256) = 0.3515625 deg. (longitude
ranges from -180 to 180)

tile height in degrees = 180 / (4 x 256) = 0.17578125 deg. (latitude
ranges from -90 to 90)

Is the above correct ? If the above is correct, it means tile widht is
bigger than tile height, why ?

Thank you

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