Gemstone Weight Calculator (Estimator)
Diamond (SG: 3.52)
Ruby (SG: 4.00)
Sapphire (SG: 4.00)
Emerald (SG: 2.72)
Quartz / Amethyst / Citrine (SG: 2.65)
Chrysoberyl / Alexandrite (SG: 3.73)
Spinel (SG: 3.61)
Topaz (SG: 3.53-3.56)
Zircon (SG: 4.70)
Garnet (Demantoid/Tsavorite) (SG: ~3.80)
Tourmaline (SG: 3.06-3.20)
Aquamarine (SG: 2.70)
Opal (SG: 2.15)
Round Faceted
Oval Faceted
Emerald / Rectangle Cut
Marquise Cut
Pear / Teardrop Cut
Heart Shape
Square / Princess Cut
Cabochon (Round/Oval)
Estimated Weight
0.00 ct
Mass in Grams: 0.00 g
How to Calculate Gemstone Weight Without a Scale
Calculating the weight of a gemstone typically requires a highly sensitive karat scale. However, when a stone is mounted in jewelry (such as a ring or pendant) and cannot be removed, or if you simply need a quick estimate based on dimensions, you can use mathematical formulas based on the gem's volume and Specific Gravity (SG).
Important: This calculator provides an estimation. The actual weight can vary based on girdle thickness, pavilion bulge, and slight variations in the stone's cut proportions.
The Gemstone Weight Formula
The universal formula for estimating the weight of a faceted gemstone is:
Length × Width × Depth × Specific Gravity × Shape Factor = Carat Weight
Understanding the Variables
- Dimensions (mm): Accurate measurements of the Length, Width, and Depth (height) of the stone in millimeters. For round stones, the Length and Width are essentially the diameter.
- Specific Gravity (SG): This is the density of the gemstone relative to water. Every gemstone variety has a unique density. For example, a 6.5mm Diamond weighs more than a 6.5mm Opal because Diamond (SG 3.52) is denser than Opal (SG 2.15).
- Shape Factor: A correction coefficient that accounts for the volume lost or gained by specific cutting styles (like the corners of an emerald cut or the tapered points of a marquise).
Common Specific Gravities (SG)
| Gemstone | Specific Gravity (SG) |
|---|---|
| Diamond | 3.52 |
| Ruby / Sapphire (Corundum) | 4.00 |
| Emerald / Aquamarine (Beryl) | 2.67 – 2.78 |
| Quartz (Amethyst, Citrine) | 2.65 |
| Topaz | 3.53 |
| Zircon | 4.60 – 4.70 |
Why Specific Gravity Matters
It is a common misconception that carat weight is a measure of size. Carat is strictly a measure of weight (1 carat = 0.2 grams). Because different gems have different densities, two stones cut to the exact same size can have drastically different carat weights. This is why a "1 carat" sapphire looks smaller than a "1 carat" diamond—the sapphire is denser, so it takes up less space to achieve the same weight.
Accuracy Factors
This calculator assumes "ideal" cut proportions. Several factors can affect the accuracy of the result:
- Girdle Thickness: A thick girdle adds weight without adding face-up size.
- Pavilion Bulge: Extra weight hidden on the underside of the stone will increase actual weight beyond the formula's estimate.
- Mounting Obstructions: If the stone is set, it may be difficult to measure the exact depth. In such cases, the calculation is only as good as the depth measurement accuracy.