to a moderately sufficient extent or degree; "the shoes are priced reasonably"; "he is fairly clever with computers"; "they lived comfortably within reason"
of no exceptional quality or ability; "a novel of average merit"; "only a fair performance of the sonata"; "in fair health"; "the caliber of the students has gone from mediocre to above average"; "the performance was middling at best"
If you describe a quality such as the size of something as middling, you mean that it is average. The Beatles enjoyed only middling success until 1963. a man of middling height. = average. of average size, quality, ability etc