Carat
Carat weight is the actual weight of the diamond once it is Cut to its finished shape. There are 100 points in a Carat, so when discussing weight it will be like talking about cents in a dollar. A stone that weighs 3/4 of a Carat will be approximately 75 points or 0.75 ct. Keep in mind that two stones of the same shape and Carat weight can look very different due to the proportions of the Cut and the shape of the stone.
Considerations when making your Carat weight selection:
Setting and overall design
Shape of the stone
For a ring, the size of the person's hand
The Cost compared with your overall budget