Real Dictionary

at least
phrase: You use at least to indicate an advantage that exists in spite of the disadvantage or bad situation that has just been mentioned.
phrase: You use at least to indicate that you are correcting or changing something that you have just said.
phrase: You use at least to say that a number or amount is the smallest that is possible or likely and that the actual number or amount may be greater. The forms at the least and at the very least are also used.
phrase: You use at least to say that something is the minimum that is true or possible. The forms at the least and at the very least are also used.

at least in American English
at the lowest estimate or figure

at least in British English
if nothing else
determiner: at the minimum