For the math question, just measure accross the widest point and add 1/2 inch {about 4in}, then measure top to bottom and add 1/2 inch {about 3 3/4in} so if you want to cut squares, then a 4 inch square ought to be just right. The addition of the 1/2 in will be enough to turn over a 1/4 inch for your 'seam' when you stitch the hexegons together. You can trim off, or leave any extra fabric around the shorter widths. If working with irregular shaped swatches you could just pin your template and cut out 1/4 inch larger than the template.