I crocheted this pattern to fit my head (about 21 inches in circumference) but it should be fairly easy to add a few stitches to make it bigger for larger heads. If need be, just add one or two more rows when making the crown of the hat (following the stitch pattern to it’s logical conclusion) and then adjust the stitch counts after appropriately. Hopefully it’s not too hard to make other sizes. :-) If it is, I can try to chart out a smaller and a larger size. I guess, if all else fails, use a bigger hook or a thicker yarn, or both if you don’t want to change the stitch counts. (or to make a smaller size, finer yarn or a smaller hook, or both)