Your answer depends on the type of stone and the cut. The measurements you give are approximate to a sort-of princess cut, but the measurements you give are not 'true' for the ratios defined by the cut.
Your local jeweler or certified gemologist can weigh the stone for you and give you its carat weight and type.
1cm = 10mm 11mm x 1cm/10mm = 1.1cm
8.5 g = 42.5 carats.
For diamonds, carat is the weight. I suspect that your 1.0 stone is a 1 carat stone. Milliliters (ml) is a measure of liquid volume, which doesn't apply to diamonds, since they are not liquid.
Carats imply weight; millimeters implies distance: they are not automatically related.
An 8mm x 8mm cushion cut is about 2.5 carats. But a jeweler or gemologist is better able to weigh the stone physically so that you have an accurate weight.
This diamond could weigh about six carats if its measurement is 10mm x 10mm.
1cm = 10mm 11mm x 1cm/10mm = 1.1cm
8.5 g = 42.5 carats.
approximately 1
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.
This stone may be in the .50 carat range, but a gemologist can weigh the stone for you and give you the carat weight.
If the diamond is a round cut, a stone weighing a little over 3 carats would have the 9.5mm measurement at the girdle.
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.
A 6mm stone would be a.75 carat diamond.
A jeweller can estimate the carat size of a stone, however, to learn its true carat weight, a stone must be removed from its setting and weighed.
1.1
The metal has a karat value, meaning that it's gold; the diamond weight is measured in carats. Since the diamond stone and the metal ring are separable, anything stamped in the metal usually refers to the metal and not to the stone mounted therein.