Dimensions for the mask pieces are 9 inches wide by 8.5 inches tall for an adult large. For an adult medium you may want to cut the pieces 8 inches wide by 7.5 inches tall.
Learn how to sew a face mask with a filter layer to donate to health care professionals. This video shows you how to sew the Masks Now pattern found at https://masksnow.org/
Find more information (including CDC guidance) on donating homemade fabric face masks here: https://www.itsalwaysautumn.com/how-to-make-a-face-mask.html