FREE pattern: http://www.crochetnmore.com/teninchdoily.htm

I specifically wanted a 10 inch diameter doily…but apparently I crochet a bit tighter (or had thinner yarn) than the pattern, so I had to add a row. To do:
Work through Row #7
Next Row: (sc1, ch7, sc1, ch2) in each chain 6 space, sl st in beginning dc.
Row #8: (Sc, ch4, sc, ch4, sc, ch3) in each chain 7 space around. FO

UPDATE For lacy edging version: work through round #7 and then work round #7plus (“next row”) as noted above. For #8 work (sc, ch4, sc, ch4, sc, ch4, sc, ch2) in each ch 7 space from the previous row. Repeat in each 7 ch space around.

Obviously changing hook sizes will have an effect on the size of the doily. The largest ecru one with lacy border used a H hook, while the smallest one in burgundy used a G hook.