Here’s some tips on how to make your diamond appear larger.
1. Consider Fancy Diamond Shapes
Fancy shaped diamonds usually look larger than round diamonds of equal weight, especially diamonds with elongated shapes, such as marquis e, oval and pear shaped diamonds. The more popular rectangular shapes like princess cuts, radiant cuts,and cushion cuts will provide you a more stretched out look that is always flattering on the finger. Be aware though that a Round Brilliant Cut is just that…Brilliant.  It will deliver more brilliance than any other cut.  A well cut Round Brilliant Cut will always deliver the brilliance you want to see and its physical presence will always be substantial, regardless of how much it weighs.

2. Choose a Pavé Setting
A pavé setting looks like a continuous surface of diamonds, but is actually made up of small diamonds set side by side into little holes, their surfaces nearly level with the setting. Tiny beads are crafted from the surrounding metal to hold the diamonds in place.

It’s difficult to distinguish individual stones, so a pavé setting makes you think the jewelry has more continuous sparkle. When a center stone is mounted on a pave’d mounting the combination of the two can be very impressive.

4. Choose an Engagement Ring with Side Stones
Small diamonds set into the band on either side of a center stone won’t necessarily make the focal diamond look larger, but can give an engagement ring more overall pizzazz.  The classic three stone configuration usually tucks the two side stones slightly up under the girdle of the center stone, giving a larger , more sparkly appearance.

5. Select a Bezel Set Diamond
Choose a diamond in a bezel setting, where a rim totally encircles the stone. White gold or platinum will blend with and enhance a white diamond, making it appear larger. A yellow gold bezel setting can throw a yellowish tint back onto the diamond.

Shallow cut diamonds look larger, but its a trade-off.

You might be tempted to buy an engagement ring set with diamonds that are cut shallow—not as deep as they ideally should be. Shallow cut diamonds do appear larger than the same size stones with a more proportional cut, but they cannot deliver the brilliance of a more ideally cut diamond. Too much light “leaks” out the back of a shallow cut diamond, dimming it’s brilliance.  The result is you get a slightly larger looking diamond, but the trade-off is a less brilliant diamond.