The perceived size of a diamond, such as your 2.5-carat diamond, can be influenced by several factors, and it may appear smaller than expected for a few reasons:

1. Diamond Shape: The shape of the diamond can significantly affect its perceived size. Some diamond shapes, like round brilliants, may appear smaller because they are deeper and have a smaller face-up area compared to elongated shapes like ovals or marquises with the same carat weight.
2. Diamond Cut: The quality of the diamond’s cut can impact how it reflects light and appears to the eye. A well-cut diamond will exhibit more brilliance and fire, making it appear larger. Conversely, a poorly cut diamond may appear smaller due to less impressive light performance.
3. Mounting and Setting: The way the diamond is mounted and set in its jewelry setting can also affect its visual size. A diamond set in a high, prominent prong setting may appear more significant than one set low in a bezel setting, even if the carat weight is the same.
4. Finger Size: The size and shape of your finger can influence how a diamond looks. A larger finger may make the diamond appear smaller in proportion, while a smaller finger may make it appear more substantial.
5. Lighting Conditions: The lighting conditions under which you view the diamond can impact its appearance. Proper lighting can enhance a diamond’s brilliance and make it appear larger, while poor lighting can have the opposite effect.
6. Personal Perception: Your expectations and personal preferences also play a role in how you perceive the size of a diamond. If you were expecting a more substantial visual impact from a 2.5-carat diamond, it might appear smaller if it doesn’t meet your expectations.

To maximize the perceived size and beauty of your 2.5-carat diamond, think about factors such as the diamond’s shape, cut quality, setting, and the lighting conditions in which you view it. Working with a skilled jeweler or gemologist can help you select the right setting and design to enhance the diamond’s appearance and make the most of its size and brilliance.