The size of the squares for a rag quilt are really up to the one making the quilt. I've seen them as small as 4" sometimes mixed with larger ones, and mine have all finished at 7" after being seamed with a 1" seam. The only size I've made are 7" with 7 across and 9 down. I think a few of the ones shown on this site have been 6" finished blocks, and some of the women have used a ½" seam instead of a 1". I think it's really up to the individual middy. No wrong or right. Just what's right for you.
We're glad to have you here middy. :)