Tool
What does a coloured stone weigh?
The same size stone weighs different carats in different minerals. A ruby is denser than a diamond, so it looks smaller for its weight.
Corundum — denser than diamond, so it looks smaller per carat.
Through the stone, top to bottom. If it is set and you cannot measure it, the estimate will be rough.
Estimated weight, ruby
Estimated from the outline and the mineral's density. Real stones vary with how they are cut, and a set stone whose depth cannot be measured varies more — this is an approximation, not a scale reading.
Weight
0.84 ct
0.168 g
Specific gravity
4.00
water = 1
Same size in diamond
0.74 ct
for comparison
Density vs diamond
1.14×
One carat, in each stone
Every stone below weighs exactly one carat, drawn to the same scale as a oval. The carat is a unit of weight, so a denser mineral spends it on fewer millimetres.
Opal
6.7 mm
Emerald
6.2 mm
Diamond
5.7 mm
Ruby
5.5 mm
Cubic zirconia
4.9 mm
This is why coloured stones are bought by millimetre rather than by carat. Asking for a one-carat sapphire to match a one-carat diamond gives you a visibly smaller stone; asking for a 5.7 mm sapphire gives you one that matches, and it will weigh about 1.14 ct.
Reference: a one-carat Ruby of this shape measures about 5.5 mm wide.Next
Weigh it, pick the karat, and see the value of the metal at the live gold price — then what a buyer is likely to hand over, which is a different number.
Sterling, coin, Britannia and fine silver at the live silver price — including why small silver items are often worth less than the trouble of selling them.
PT950, PT900 and PD950 at live prices. Both metals are denser than gold, which is why the weight surprises people.