These gemstones weigh the same: one carat.
A 625 carat diamond refers to a diamond that weighs 625 carats. Carat is a unit of measurement for gemstones, with one carat equal to 200 milligrams. A diamond of this size would be considered extremely rare and valuable.
The two measurements you give are not related, essentially. The MM measurement could be the diameter of a brilliant cut diamond, or one measurement of another shape. The carat weight you give is a weight measurement of gemstones.
For a diamond of this natural colour and size, you are best advised to shop among auction houses, because it is a rare and expensive diamond. As an example, a 23 carat pink, the Graff Pink, below, sold recently for almost US$50,000,000. Also below, you can shop online for a natural pink diamond, the largest of which is just over 3 carats, and price the one you want to buy.
Although 90% of women never get a diamond over 1 carat, there are many sizes and shapes that diamonds can be cut into. Jewelers can cut a diamond to any size or shape. The largest cut diamond in the world is the Centenary, which holds the record at 273 carats. Before it was cut, it weighed 520 carats.
In 1668 Jean Baptiste Tavernier, a French traveler and gem merchant, sold a blue diamond weighing 112 3/16 carats (more than twice the size the diamond is today) to King Louis XIV of France. Tavernier would say only that the diamond had come from India. Louis XIV had the gem recut and set as a pendant as part of the crown jewels.
A carat diamonds size is 3.5mm.
The size of these two objects is exactly the same: 5mm.
The carat size of a diamond should be determined by a certified jeweler. There are two different sizes the is the millimeter size which as stated was 7mm and then a jeweler can give a carat size.
The diamond weighs 40/100ths of a carat. Other measurements depend on the style of its cut.
Carat is a weight measurement for a diamond: here size matters -- bigger is better, biggest is best.
A two carat round brilliant cut stone will measure about 8.2 mm. A different cut will have a different measurement.
A 625 carat diamond refers to a diamond that weighs 625 carats. Carat is a unit of measurement for gemstones, with one carat equal to 200 milligrams. A diamond of this size would be considered extremely rare and valuable.
One carat equals 100 in this example. If the diamonds are of equal size, then each diamond weighs 4.5454545 carats.
One carat weight of diamond weighs .20 grammes, so your diamond is about half that weight, or roughly half a carat.
If 7.7 is the carat weight, then the size is 7.7 carats. The millimeter measurements of a diamond with this weight will vary, depending on the cut.
A diamond is valued by its cut, clarity, carat weight and colour. A local jeweler can show you stones in this category.
You can review the chart, below, to determine the specific gravity of diamond versus other gemstones, including several different types of rubies. From the chart you can deduce that depending on the type of ruby, it may or may not be exactly comparable to diamond.