Diamond size is often discussed using both carat weight, which measures weight, and millimeters (mm), which measure physical dimensions. Millimeter measurements are especially useful when you want to compare how large two stones may look from above. SKJ product pages do not assume or generate diamond measurements: ask the team to verify the measurement for the exact diamond when it matters to your decision.
Carat weight vs. millimeter size
One carat equals 0.2 grams, so carat is a weight unit rather than a diameter. Diamonds of the same carat weight can have different face-up measurements because their shape and proportions differ. Millimeter measurements let you compare actual dimensions instead of using weight as a visual-size shortcut.
A general reference for round brilliant diamonds
Round brilliant diamonds with typical proportions often fall near the approximate ranges below. These are educational references, not specifications for any SKJ product, and an individual diamond should be measured or checked against its own report where applicable.
- About 3.0 mm can be near 0.10 carat.
- About 4.0 mm can be near 0.25 carat.
- About 5.0 mm can be near 0.50 carat.
- About 6.5 mm can be near 1.00 carat.
- About 7.4 mm can be near 1.50 carat.
- About 8.1 mm can be near 2.00 carats.
Treat these as orientation only. Shape, depth, girdle and other proportions can shift the relationship between weight and visible dimensions.
For non-round diamonds, compare both dimensions
Oval, marquise, emerald-cut, cushion and other shapes are not described well by one diameter. Length and width together give a clearer idea of outline and face-up scale. Two stones with the same weight can have noticeably different length-to-width proportions and visual presence.
How to choose a size for jewelry
- Look at proportion. Compare the stone with the ring, pendant or earring design rather than judging the number alone.
- Think about daily wear. A larger or higher setting can feel different in everyday use.
- Confirm the setting. The setting needs to suit the exact stone and design.
- Compare the complete price. Ask for the current price of the exact diamond and jewelry configuration rather than extrapolating from a different size.
Millimeters and GIA reports
When a GIA report applies to a diamond, measurements are part of the identifying information on the report. That can help you compare visible dimensions with carat weight while keeping the information tied to the exact stone. Read our GIA diamond report guide for more context.
Compare sizes in person when possible
Photos and numbers are useful for narrowing choices, but they do not fully show how a diamond looks against a particular hand or setting. If you are deciding between sizes, compare physical examples at the Sok Kheang Jewelry showroom in Phnom Penh and ask the team to verify the exact measurements before you decide.