Diamond Equivalent Weight Calculator
Quick answer
At the same size, weight follows density. A stone cut to the size of a 1 ct diamond weighs about 1.14 ct in sapphire, 0.91 ct in moissanite and 1.65 ct in CZ. "DEW" means a moissanite is sold by the diamond weight its size matches, not its own weight.
Same-size figures use the pure density ratio. Data verified .
Compare weight and size across materials
Diamond equivalent weight, in plain words
Diamond equivalent weight (DEW) answers a simple question: "If this stone were a diamond of the same size, what would it weigh?" It is a size label borrowed from the diamond market, because shoppers know roughly what a 1 carat diamond looks like.
Moissanite is the main material sold this way. It is lighter than diamond, so a moissanite cut to diamond's 1 carat size really weighs less than 1 carat. Rather than list a stone as "0.9 ct" and confuse buyers comparing sizes, sellers label it "1 ct DEW".
Why the same size weighs different amounts
Every material has a density, which gemologists call specific gravity (SG). It tells you how heavy the material is compared with the same volume of water. Diamond is 3.52. Moissanite is 3.22. Sapphire is 4.00. CZ is about 5.80. Cut each of them to exactly the same shape and size and their weights will follow the same ratios.
The maths is short: weight of material X = diamond weight x (SG of X / 3.52). The tool runs this for every common material and shows the range that comes from each material's natural variation in SG.
Same weight, different size
The flip side matters just as much for shoppers. At the same carat weight, denser stones are smaller. A 1 ct round CZ is about 5.4 mm across, roughly 15% smaller in diameter than a 1 ct diamond at 6.5 mm. A 1 ct emerald is about 6.9 mm, about 9% bigger.
Size differences look smaller than weight differences because diameter only changes with the cube root of volume. A material 15% denser is only about 5% smaller across.
Moissanite has two honest weights
For moissanite you will often see two numbers, and both can be correct:
- The density figure. Same size as a 1 ct diamond, multiplied by 3.22 / 3.52, gives about 0.91 ct. This is what our calculator shows.
- The seller's figure. Many sellers publish lower real weights, for example 0.88 ct for a 6.5 mm round. That is consistent with moissanite being cut a little shallower than the ideal diamond the formula assumes. We report this as a published convention, not as a measured fact.
If the real weight matters to you, for example for insurance or resale, ask for the weighed figure. More detail on the moissanite vs diamond size page and the moissanite size chart.
Using the comparison as a buyer
- Find out whether a listed weight is real or equivalent. Look for "DEW", "diamond equivalent", "DEW ct" or "ct DEW".
- Turn the weight into millimetres with the carat to mm finder. Size is what you see on the hand.
- When comparing a diamond with a colored stone, compare millimetres, not carats. A 1 ct sapphire and a 1 ct diamond are not the same size.
Lab-grown and natural diamonds are the same material, so the comparison between them is simple: same weight, same size. See lab-grown vs natural diamond size.
Related questions
What does DEW mean on a moissanite listing?
DEW stands for diamond equivalent weight. A "1 ct DEW" moissanite is cut to the size of a 1 ct diamond, about 6.5 mm round. It does not weigh 1 ct. By density alone it weighs about 0.91 ct.
Is 1 carat moissanite the same size as 1 carat diamond?
If the 1 ct is a DEW figure, yes, that is the whole point of DEW. If it is a real weight of 1.00 ct, the moissanite is a little larger: about 6.6 mm against 6.5 mm.
How heavy is a sapphire the size of a 1 carat diamond?
About 1.14 ct. Sapphire (SG 4.00) is denser than diamond (SG 3.52), so the same volume weighs more.
Does a 1 carat emerald look bigger than a 1 carat diamond?
Yes. A 1 ct emerald has the volume of a 1.29 ct diamond, because emerald is much lighter.
Do lab-grown diamonds need a DEW figure?
No. Lab-grown diamond is the same material as natural diamond, with the same density, so its real weight and its "diamond equivalent" are the same number.
Is DEW used for anything besides moissanite?
Sometimes for CZ and other simulants, and occasionally for colored stones in a mixed piece. Whenever you see "equivalent" next to a weight, it describes size, not real weight.
Why does the seller say my moissanite weighs less than your estimate?
Moissanite is often cut with different proportions from the round brilliant diamond the formula assumes. A shallower cut puts less material under the same face-up size. A scale settles it.
Which is heavier at the same size, CZ or diamond?
CZ, by a lot. A CZ cut to the size of a 1 ct diamond weighs about 1.65 ct.
Sources and method
Weight estimates use the colored-stone shape factors published by the International Gem Society and the Dendritics standard formula, and the diamond trade constants and length to width ratio tables published in jewelry trade references (Esslinger, Omni, Octonus). Specific gravity values are cross-checked against the International Gem Society density tables, the USGS Natural Gemstones report and GemSelect. Seller DEW conventions for moissanite are reported as published by sellers and are not independently verified.
Every number on this page is generated by the same formula engine as the calculators. Read the full method, constants and limits and the editorial policy. Data last verified 2026-11-04.
Estimates only. This is not an appraisal, grading report or valuation. A calibrated scale or a lab report is the only real weight.