Lab-Grown vs Natural Diamond Size
Quick answer
Lab-grown and natural diamonds are the same material with the same density (SG about 3.52), so at the same carat weight and cut they are the same size. A 1 ct round of either is about 6.5 mm across. Differences in look come from the cut, not from where the diamond formed.
Round brilliant at 61% depth. Data verified .
Same material, same size
A lab-grown diamond is not an imitation. It is carbon arranged in the diamond crystal structure, grown in a laboratory instead of in the earth. Because the material is the same, its specific gravity is the same, and specific gravity is what links weight to size.
Our engine treats them identically. A diamond cut to the same size as a 1 ct natural stone, if lab-grown, weighs 1.00 ct; the natural stone weighs 1.00 ct. At 1 ct each, their round diameters are 6.45 mm and 6.45 mm.
Worked example
Measure a 6.5 mm round that is 4.0 mm deep. As a natural diamond, the estimate is 1.03 ct (range 0.98 to 1.12). As a lab-grown diamond, it is 1.03 ct (range 0.98 to 1.12). Identical, as they should be.
| Carats | Natural | Lab-grown |
|---|---|---|
| 0.25 ct | 4.1 mm | 4.1 mm |
| 0.50 ct | 5.1 mm | 5.1 mm |
| 1.00 ct | 6.5 mm | 6.5 mm |
| 1.50 ct | 7.4 mm | 7.4 mm |
| 2.00 ct | 8.1 mm | 8.1 mm |
| 3.00 ct | 9.3 mm | 9.3 mm |
What can make two diamonds of the same weight look different
- Depth. A deep stone hides weight under the girdle and faces up smaller.
- Girdle thickness. A thick girdle adds weight without adding face-up size.
- Shape. Ovals, pears and marquises look larger than rounds of the same weight. Princess cuts look smaller.
- Setting. Prongs, halos and bezels change how big a stone appears.
None of these depend on whether the diamond is natural or lab-grown. Our guide to why the same carat weight looks different covers each with numbers.
Reading listings
Lab-grown diamond listings use real weight, just like natural diamond listings. You should not see DEW on a lab-grown diamond. If a listing calls a stone "lab diamond" and gives a DEW figure, it may be moissanite or another simulant, so ask for clarification and a grading report.
Grading reports from major labs list measurements for both natural and lab-grown stones. Those measurements are more useful than any chart. Put them into the mm to carat calculator as a sanity check.
Scope of this page
This page is about size and weight only. Price, value and market questions are outside the scope of this site and we do not comment on them. For size across all diamond shapes, see the diamond size chart. For moissanite, see moissanite vs diamond size.
Related questions
Is a 1 carat lab-grown diamond the same size as a natural 1 carat diamond?
Yes, if both are cut to the same proportions. Both are about 6.5 mm round at typical depth.
Do lab-grown diamonds weigh less?
No. Lab-grown diamond is carbon in the same crystal structure as natural diamond, with the same density (SG about 3.52).
Why do lab-grown diamonds often look bigger for the money?
That is a price question, not a size question. At the same weight they are the same size. Price differences are outside the scope of this site.
Can I use a diamond size chart for lab-grown diamonds?
Yes. Every chart and calculator on this site treats them identically.
Are lab-grown diamonds the same as moissanite or CZ?
No. Moissanite and CZ are different materials with different densities, so their sizes per carat differ. Lab-grown diamond is diamond.
Do lab-grown diamonds come in the same shapes?
Yes. Rounds, ovals, cushions, emerald cuts and every other diamond shape are produced, and the same shape formulas apply.
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.
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.