Cubic Zirconia (CZ) Carat to mm Chart
Quick answer
A 1 carat round cubic zirconia is about 5.4 mm across and a 2 carat about 6.8 mm. A 1 ct oval is about 6.5 x 4.7 mm. With a specific gravity of 5.80, cubic zirconia looks smaller than a diamond of the same carat weight.
Typical depth and outline assumed; deep-cut stones face up smaller. Data verified .
Cubic zirconia carat to mm calculator
Cubic zirconia size by carat weight
Cubic zirconia (CZ) is a lab-made material that has been used to imitate diamond since the 1970s. It is far denser than diamond, so a CZ of the same carat weight is much smaller.
That catches out many shoppers. Because CZ is usually sold by millimetre size, some listings state a "carat" figure that really means the weight of a diamond of the same size. Others state the real CZ weight. The two can differ by more than half again.
| Carats | Round | Oval (1.4 ratio) | Cushion | Diamond round, same weight |
|---|---|---|---|---|
| 0.25 ct | 3.4 mm | 4.1 x 2.9 mm | 3.3 mm | 4.1 mm |
| 0.50 ct | 4.3 mm | 5.2 x 3.7 mm | 4.1 mm | 5.1 mm |
| 0.75 ct | 4.9 mm | 5.9 x 4.2 mm | 4.7 mm | 5.9 mm |
| 1.00 ct | 5.4 mm | 6.5 x 4.7 mm | 5.2 mm | 6.5 mm |
| 1.50 ct | 6.2 mm | 7.5 x 5.3 mm | 5.9 mm | 7.4 mm |
| 2.00 ct | 6.8 mm | 8.2 x 5.9 mm | 6.5 mm | 8.1 mm |
| 3.00 ct | 7.8 mm | 9.4 x 6.7 mm | 7.4 mm | 9.3 mm |
| 4.00 ct | 8.6 mm | 10.4 x 7.4 mm | 8.2 mm | 10.2 mm |
| 5.00 ct | 9.2 mm | 11.2 x 8.0 mm | 8.8 mm | 11.0 mm |
Generated by our formula engine at typical depth: 61% of width for rounds and ovals, 70% for cushions. Round sizes carry a range of about plus or minus 3% that comes from the spread in published factors and in cubic zirconia density (5.60 to 6.00).
Cubic zirconia compared with diamond
Cubic zirconia has a specific gravity of 5.80 against 3.52 for diamond. At the same carat weight, a cubic zirconia is smaller than a diamond, by about 15% in diameter. Put the other way round, a cubic zirconia cut to the size of a 1 ct diamond weighs about 1.65 ct.
Use the diamond equivalent weight calculator to compare cubic zirconia with diamond, moissanite and other gems side by side, or the mm to carat calculator if you have a stone to measure.
Common cubic zirconia shapes
Every shape is available and cut to calibrated millimetre sizes. Rounds and princess cuts are most common for engagement-style pieces.
Buying notes
- Ask whether a stated CZ carat weight is real weight or diamond equivalent. A "1 carat" CZ that is the size of a 1 ct diamond really weighs much more.
- Order CZ by millimetres when you are matching a setting.
- CZ is 8 to 8.5 on the Mohs scale. It can show wear and lose sparkle over years of daily wear, and is easy to replace.
- CZ is a simulant, not a diamond. Honest listings say so clearly.
Cubic zirconia at a glance: specific gravity 5.80 (range 5.60 to 6.00), Mohs hardness 8 to 8.5. IGS lists a slightly wider range (5.34 to 6.00). Much denser than diamond.
Other gemstone size charts
- Sapphire Carat to mm Chart
- Ruby Carat to mm Chart
- Emerald Carat to mm Chart
- Amethyst Carat to mm Chart
- Topaz Carat to mm Chart
- Garnet Carat to mm Chart
- Aquamarine Carat to mm Chart
- Spinel Carat to mm Chart
- Diamond size chart in mm
- Gemstone specific gravity chart
Related questions
How many mm is a 1 carat cubic zirconia?
About 5.4 mm for a round at typical depth, likely 5.2 to 5.6 mm. A 1 ct oval cubic zirconia is about 6.5 x 4.7 mm.
How big is a 2 carat cubic zirconia?
A 2 ct round cubic zirconia is about 6.8 mm, and a 2 ct oval cubic zirconia with a 1.4 ratio about 8.2 x 5.9 mm. At 3 ct, a round cubic zirconia reaches about 7.8 mm.
Is a 1 carat cubic zirconia bigger than a 1 carat diamond?
A 1 ct cubic zirconia is smaller than a 1 ct diamond: 5.4 mm against 6.5 mm round, about 15% smaller across. In volume it matches a 0.61 ct diamond.
How much does a cubic zirconia the size of a 1 carat diamond weigh?
A cubic zirconia cut to that size weighs about 1.65 ct, because weight at the same size follows density (SG 5.80 for cubic zirconia against 3.52 for diamond).
How much does a CZ the size of a 1 carat diamond weigh?
Much more than 1 ct. Use the DEW calculator for the exact estimate with its range.
Is cubic zirconia the same as zircon?
No. Zircon is a natural mineral with its own, different density. Cubic zirconia is a lab-made material.
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.