SkubaK, figure you need 168 little tiny squares of each piece that make the 4 piece. 168 squares divided by 20 per strip gives you 8.4 strips so cut 9 strips of each (if you're using different shades of purple for each tiny square within the 4 patch). If you're using the same fabric for both lavender pieces and the same fabric for both purple pieces (like Jeanne S did in post 693 above), 17 strips of each color will give you enough tiny squares.