I've measured that my OCZ Vertex 2 SATA II SSD has a diagonal of 17 cm. The Google calculator says that 17 cm is 6.69 inch, not even near to 2.5 or 1.8 inch. The OCZ product page says that the drive is 2.5 inch.

Am I doing it the right way by measuring the diagonal? Or should I take the width? 7 cm is 2.76 inch, but 2.5 inch is 6.35 cm.