carat vs. color  length*  width*

(or examine a single gem)
* size in mm (optional)

4 Ct Amethyst (Cushion)


4 Ct Quartz (Round)

yellowish green
10.18×10.18 mm 10.89×10.89 mm
actual size
Actual size of 4ct Amethyst   Actual size of 4ct Quartz
Actual size is set for screen Change
Ring: Skin tone:
Ring width: 3.0 mm
Left finger image
Ring on left finger
Purple 4ct Amethyst on a ring
64 mm
Right finger image
Ring on a right finger
Yellowish Green 4ct Quartz on a ring
Your settings
Skin tone
Ring diameter
16.9 mm
Ring width
3.0 mm
Finger length
64 mm
Ring diameter: 16.9 mm
Actual sizes of 4ct Amethyst Cushion (10.18×10.18mm, Purple) and 4ct Quartz Round (10.89×10.89mm, Yellowish Green) as they would appear on a ring and finger. Adjust the ring and finger size to get an idea of how these gemstones would look on your finger.

Where to buy?

For Amethyst or Quartz check what Amazon has to offer. You'll usually find quite a selection from many different vendors. Worth a check. For other high quality gemstones (Rubies, Saphhires, Emeralds) and especially Diamonds, I highly recommend JamesAllen.

Face-up Size

Amethyst and Quartz 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.

4 Ct Amethyst (Cushion) 4 Ct Quartz (Round)
10.18×10.18 mm vs 10.89×10.89 mm
93.27 mm²   93.14 mm²
Face-up size outline
Face-up size outline
4ct Amethyst Cushion (10.18×10.18mm)
4ct Quartz Round (10.89×10.89mm)
Difference: 0.1% (0.13 mm²)
4ct Amethyst Cushion (10.18×10.18mm) has approx. 0.1% more face-up area than 4ct Quartz Round (10.89×10.89mm).

Popular comparisons:

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Actual size is currently adjusted to screen.

If your screen (phone, tablet, or monitor) is not in diagonal, then the actual size of a gem, ring and finger will not be shown correctly.