Beryl and Emerald have the same specific gravity so their face-up size
depends on the weight, shape and proportions of the cut. Face-up area is a measure of the size of the gem when viewed from above (as set in a ring).
It tells you how big the gem is at the girdle plane.
1 Ct Beryl (Round)
1 Ct Emerald (Emerald)
6.82×6.82 mm →
36.49 mm² ← 7.28×5.39 mm
1ct Beryl Round (6.82×6.82mm)
1ct Emerald Emerald (7.28×5.39mm)
Difference: 0.1% (0.04 mm²)
1ct Beryl Round (6.82×6.82mm) has approx. 0.1% more face-up area than 1ct Emerald Emerald (7.28×5.39mm).