Originally Posted by imsewnso

http://www.youtube.com/watch?v=LZgv3vwv

in this tutorial you fold the fabric in half and measure 1" down the side and 2" along the fold for a 10" bowl (join the dots and sew to make a dart.) for 15" it is 1 and 3 and for a 12" it is 1 and 2.5. Hope this helps.