... alternately, 'less than or equal to'?
If nothing exists, can you suggest something new to be widely adopted?
The term at least is close in meaning to greater than or equal to. Example of usage:
Similarly, the term at most is close in meaning to less than or equal to. Example of usage:
The trick with these phrases is to find the phrase that means the opposite and then invert it.
If something is greater than or equal to something then the opposite must be less than. So inverted would be not less than.
If it's less than or equal to then the inverted opposite would be not more than or sometimes no more than.
Alternatively you can take the equal to value and imply an acceptable variance direction. For instance at least X would be equal to or greater than X and at most Y would be equal to or less than Y.
Phrases like up to Z can be somewhat ambiguous and could include or exclude Z.