An important point is that it isn't the key the song's in that dictates the range a song is in, it's the highest and lowest notes. A key cannot dictate the range, but in order to put the range of a song into something comfortable to sing, its key may have to be changed. If you've written a song in, say, C, and the vocalist says it's too high to sing, it will need taking down, maybe to Bb, A, or even lower. Then the problem may be that the low notes are not easy to sing. In this case, the whole range of the song may be too great for that singer.
Each singer will have their own comfortable range in which to sing. That's from a good low to a good high note. A singer cannot say they always sing in Eb, or G, or whatever.(Although I have heard 'singers' say that). Each song will have its individual highest/lowest note,- its range. Not its tessitura, that's subtly different.
Another aspect is - what voice is it written for? Soprano, alto, tenor or bass? And some who are, say, tenors, will have a greater vocal range than others, so it's not cast in stone. There are suggested highest/lowest notes for each voice, but everyone varies. If you make your song an octave and a half range, in whatever key, that's usually o.k. for most, but you may well have to change the key of the whole song if it's an alto singing instead of, say, a soprano.
For an insight into an answer, you could check out as many songs as you like, noting each one's highest and lowest notes. Then check the key of each, out of interest. Most pop type songs will have not a large range, as they are designed to be sung by the fans, whose ranges may well not be huge.