The weight of diamonds is measured in carats. We understand that most people find it hard to imagine what it is. And if you ask them what a 3-carat diamond looks like, for example, they will have difficulty answering.
One carat equals 0.2 grams
Why so much? The answer is in history. People traded in diamonds back in the old days, when there were no exact instruments for measuring, there were only usual scales with two bowls. In order to measure the weight of the stone, it was necessary to come up with something that could be put on another scale. Something small, consisting of many parts, absolutely identical in weight (because no one wanted it to be cheated!). That's when the merchants thought of the Ceratonia siliqua acacia seeds, which have almost the same weight - 0.2 grams. This is where the concept of "carat" came from.
In today's world
Mass is still better measured on an electronic weigher. Diamonds of the same diameter may have different weights. If you take a stone with ideal proportions, the diameter of a 1-carat round diamond is 6.4 mm. But if the proportions have been broken, it can change in both sides. Contrary to popular belief, mass is not a defining parameter for a diamond. If you take two stones of the same color and clarity, the larger one will be more expensive. But if a small stone is fully transparent and has no inclusions, it will be valued higher than a large one, but with yellowish or inclusions.
The largest diamond in history is a 545.67 carat yellow-brown diamond called the Golden Jubilee. It was cut from a 755.5-carat diamond found in South Africa in 1985.