Your answer depends on the cut you are measuring. If the gem is a round cut, the carat weight will be about .10 carats.
The largest cut emerald gem is called the Mogul Emerald found in 1965 weighs in at 217.80 carats and is 10cm tall. A 4.5-inch vase that was carved from a single emerald crystal weighing 2,205 carats resides in the Viennese Treasury. The "Duke of Devonshire" a hexagonal prism, 5 cm in diameter by 6 cm in height weighing 1,383.95 carats is uncut crystal from Muzo, Colombia. The Bahia emerald is a 180,000 carat, 850 pound emerald cluster is said to be the second largest emerald ever found.
A round cut diamond weighing .25 carats measures 4.1mm at the girdle.
If the cut is round, this weight may rate in the just under 7 carats range. If it is a different cut, the weight will be different.
A round cut diamond weighing .25 carats measures 4.1mm at the girdle.
This diamond could weigh about six carats if its measurement is 10mm x 10mm.
The mm size of a diamond stone relative to its weight in carats is directly related to the cut and the excellence of the cut. For example, a round brilliant stone measuring 8 mm in diameter at the girdle weighs about two carats. A different cut will have a different weight in carats.
It depends on the cut, clarity, color, size, and other factors. A large, single emerald is worth more than a collection of stones that total six carats. Emeralds are worth less if they are heavily flawed or treated to hide flaws. A single stone of this size may be worth very little compared to a perfect emerald one-tenth the size.
One kilo equals 5,000 carats regardless of the colour or cut of diamond.
If the diamond is a round cut, a stone weighing a little over 3 carats would have the 9.5mm measurement at the girdle.
Carat for carat, we usually see a diamond costing more than an emerald. That's a generalization, but it quite accurate. Carats (carat weight or size), cut, color and clarity are the variables that determine price.
Carats indicates weight; mm indicates length and width -- the two are not necessarily compatible. However, if your diamond is a round brilliant cut diamond and its diameter at the girdle is 10mm, the diamond may be about four carats. If the cut is another shape, it may have a different carat weight.