An enduring needlepoint problem is circles. While there are ways to make large ones, as seen in this article from ANG’s site, small circles defeat many stitchers.
Jean Hilton developed a wonderful stitch for making circles called Jessica and now Orna Willis has helped us conquer them with a new How to on her site. This simple how to clearly shows the stitch.
To change sizes, change the number of stitches on each side which will also change the length of the stitches.
The circle is formed by the way the stitches cross each other and twist around.
From this you get pretty raised circles.