At the same weight a emerald covers about 10% more of the finger. Same carat, same price bracket, visibly different stone.
The reason is proportion, not quality. A emerald runs about 1.40:1 long to wide; a radiant about 1.20:1. Weight spent on length is weight you can see. Weight spent on depth sits below the setting, where it does nothing for appearance.
| Carat | Emerald (mm) | Emerald area | Radiant (mm) | Radiant area |
|---|---|---|---|---|
| 0.25 ct | 4.55 × 3.25 | 14.3 | 4.03 × 3.36 | 13.0 |
| 0.5 ct | 5.73 × 4.10 | 22.7 | 5.08 × 4.23 | 20.7 |
| 0.75 ct | 6.56 × 4.69 | 29.8 | 5.81 × 4.84 | 27.1 |
| 1 ct | 7.22 × 5.16 | 36.1 | 6.39 × 5.33 | 32.8 |
| 1.25 ct | 7.78 × 5.56 | 41.9 | 6.89 × 5.74 | 38.1 |
| 1.5 ct | 8.27 × 5.91 | 47.3 | 7.32 × 6.10 | 43.0 |
| 2 ct | 9.10 × 6.50 | 57.3 | 8.06 × 6.71 | 52.1 |
| 2.5 ct | 9.80 × 7.00 | 66.4 | 8.68 × 7.23 | 60.4 |
| 3 ct | 10.42 × 7.44 | 75.0 | 9.22 × 7.69 | 68.2 |
An elongated shape also reads longer on the finger, which is a separate question from area. Whether that suits a particular hand is not something a table can settle — which is exactly why it is worth putting the two on your own photograph, at the same scale, and looking.