Question: how big are diamond carats?
Answer: As you can see above, the size of a 1 carat diamond is approximately 6.5mm (based on the assumption that the stone is cut to ideal proportions). On the other hand, the size of a . 5 carat diamond is approximately 5.2mm. Even though the carat weight is 50% of a 1 carat stone, it doesn't face up twice as small!