💎 Gemstone Weight Calculator
Estimate a stone's carat weight from its measured length, width, and depth, its gem type (specific gravity), and its cut — no need to unmount or weigh it.
📐 Measure, Choose the Gem, Estimate the Carats
What is a Gemstone Weight Calculator?
It estimates how many carats a stone weighs from its dimensions, without taking it out of the setting. Enter the length, width, and depth, pick the gem (which sets its specific gravity) and the cut (which sets a fill factor), and it computes the mass and converts to carats.
Use it to sense-check a listing, appraise an heirloom you can't unmount, or compare stones by size. It's an approximation shaped by the exact proportions and girdle, so for a precise figure, weigh a loose stone on a carat scale.
❓ Frequently Asked Questions
How is carat weight estimated from measurements?
The tool computes volume from the length, width, and depth (in cm), multiplies by the gem's specific gravity to get mass in grams, and applies a shape 'fill factor' for how much of the box the cut actually fills. Carat weight is then mass ÷ 0.2, since one carat equals 0.2 grams.
What is specific gravity and why does it matter?
Specific gravity is a gem's density — how much a given volume weighs. Diamond is about 3.52, ruby and sapphire about 4.00, and emerald about 2.72. A denser stone of the same size weighs more, so using the right value (or your own measured one) is key to an accurate carat estimate.
Why does the shape or cut change the estimate?
A cut stone never fills its bounding box completely. A brilliant round leaves more empty corners than a step-cut emerald or a rectangle, so each shape uses a different fill factor. Choosing the correct shape keeps the estimate realistic rather than over- or under-stating the weight.
How accurate is this compared with weighing the stone?
It's a close approximation — real weight depends on the exact proportions, girdle thickness, and any bulge below the setting. Use it when you can't unmount or weigh the gem. For an exact figure, weigh a loose stone on a carat scale.