The Master Conversion Chart
Your comprehensive technical guide to moissanite millimetres, Diamond Equivalent Weight (DEW), and New Zealand ring sizing.
Understanding Moissanite Measurements
When shopping for fine jewellery at Miozuki, you may notice that moissanite is often described by its physical dimensions in millimetres (mm) rather than its carat weight. This is a crucial distinction for both technical accuracy and consumer transparency. While diamonds are traditionally sold by weight (carats), moissanite is a unique gemstone with its own physical properties.
The primary reason for using the Diamond Equivalent Weight (DEW) is the difference in density between the two stones. Moissanite is approximately 10% to 15% lighter than a diamond of the same size. Therefore, a moissanite stone that measures 6.5mm, the standard size for a 1.00-carat round brilliant diamond, will actually weigh significantly less on a scale. To help our New Zealand customers compare visual size effectively, the DEW system provides a familiar reference point.
Technical Fact: Density Comparison
The specific gravity (density) of a diamond is approximately 3.52 g/cm³, whereas the specific gravity of moissanite is approximately 3.22 g/cm³. This scientific variance means that if you were to buy a 1.00-carat moissanite by weight alone, it would physically look much larger than a 1.00-carat diamond. By using DEW, we ensure that when you order a 1.00ct DEW stone, it fits perfectly into settings designed for 1.00-carat diamonds.
Round Brilliant Moissanite Conversion Chart
The Round Brilliant cut is the most popular choice for engagement rings and studs. Below is the master conversion guide for round stones, ranging from subtle accents to statement centrepieces.
| Millimetre Size (mm) | Diamond Equivalent Weight (DEW) | Estimated Actual Weight (ct) | Best Used For |
|---|---|---|---|
| 4.0 mm | 0.25 ct | ~0.23 ct | Subtle Studs / Side Stones |
| 5.0 mm | 0.50 ct | ~0.46 ct | Minimalist Solitaires |
| 6.0 mm | 0.85 ct | ~0.78 ct | Classic Engagement Rings |
| 6.5 mm | 1.00 ct | ~0.91 ct | Standard 1-Carat Look |
| 7.0 mm | 1.20 ct | ~1.10 ct | Premium Solitaire |
| 7.5 mm | 1.50 ct | ~1.35 ct | Impressive Brilliance |
| 8.0 mm | 2.00 ct | ~1.80 ct | Bold Statement Rings |
| 9.0 mm | 2.70 ct | ~2.26 ct | Luxury Premium |
Fancy Cut Conversion Guide
Fancy shapes like ovals, pears, and princess cuts carry their weight differently. An oval moissanite often provides a larger face-up appearance than a round stone of the same weight, making it an excellent choice for those wanting to maximise their visual impact on a budget.
Oval Cut (Length x Width)
| Dimensions (mm) | DEW (Carats) |
|---|---|
| 6 x 4 mm | 0.50 ct |
| 7.8 x 5.7 mm | 1.00 ct |
| 8.5 x 6.5 mm | 1.50 ct |
| 9.61 x 7.1 mm | 2.00 ct |
| 11 x 8 mm | 3.00 ct |
Princess Cut (Square)
| Dimensions (mm) | DEW (Carats) |
|---|---|
| 4.0 mm | 0.40 ct |
| 5.0 mm | 0.75 ct |
| 5.5 mm | 1.00 ct |
| 6.5 mm | 1.50 ct |
| 7.0 mm | 2.00 ct |
New Zealand Alphabetical Ring Sizing
In New Zealand, we use the British/Australian alphabetical ring sizing system. Finding the perfect moissanite stone is only half the journey; ensuring a comfortable fit is essential for a lifetime of wear. If you are unsure of your size, we offer a $1 ring sizer that includes a credit (ring sizer plus shipping) toward your future custom or bespoke ring order.
For the full mm, diameter, and NZ-to-US size conversion, see our ring size converter. Half sizes (e.g. M½) are also available for many of our bespoke designs to ensure the ultimate fit.
Why Accurate Conversion Matters
Choosing the right stone size involves more than just aesthetics. For residents in NZ looking for accessible luxury, understanding the mm to DEW conversion ensures:
- Proportion: knowing how a 7mm stone will sit on a Size M finger.
- Budgeting: moissanite offers a significantly higher size-to-price ratio than diamonds, but comparing them accurately requires DEW data.
- Setting Integrity: if you are purchasing a loose stone for an existing setting, the millimetre measurement is the only metric that guarantees a fit.
Miozuki is committed to accessible luxury. By providing this master chart, we empower our customers to make informed decisions that align with their personal style and ethical values.
The Science Behind the Sparkle: Why Millimetres Matter
When selecting a moissanite stone, the millimetre measurement provides a true indication of the stone's surface area. In the world of optics, this is known as the face-up size. Unlike carats, which measure mass, millimetres measure geometry. This is vital because two stones with the same carat weight could have different millimetre measurements depending on how deep or shallow they are cut. A deep-cut stone hides its weight in the bottom (pavilion), while a shallow-cut stone might look large but lack the brilliance and fire moissanite is famous for.
Miozuki ensures that all our moissanite stones are cut to ideal proportions. By adhering to the standards in our Master Conversion Chart, we guarantee that the fire (dispersion) and brilliance (refractive index) of our stones are maximised. Moissanite actually has a higher refractive index (2.65 to 2.69) than a diamond (2.42), meaning it reflects more light and produces more rainbow flashes. When you choose a stone based on our mm-to-DEW chart, you are choosing a stone optimised for these incredible optical properties.
Whether you are in Auckland, Wellington, Christchurch, or anywhere else in Aotearoa, our goal is to provide a transparent, luxury experience. Using the Diamond Equivalent Weight allows you to compare our ethical, lab-grown gemstones directly with traditional mined diamonds, highlighting the exceptional value moissanite provides without compromising on the visual scale of your jewellery.
Frequently Asked Questions
Why is moissanite lighter than diamond?
Moissanite is a different mineral (silicon carbide) than diamond (carbon). Its molecular structure is less dense, meaning that while it looks identical or even more brilliant to the naked eye, it weighs less than a diamond of the same physical volume.
Will a 1ct DEW moissanite fit in a diamond setting?
Yes. Because DEW is calculated based on the physical dimensions (e.g. 6.5mm for a 1ct round), a 1ct DEW moissanite will fit perfectly into a standard 1-carat diamond setting.
How do I measure my ring size at home?
While there are DIY methods using string or paper, they are often inaccurate. We highly recommend ordering our $1 ring sizer from the Miozuki store. It is the most reliable way to find your NZ alphabetical size before ordering.
What is the most popular moissanite size in New Zealand?
The 1.5ct DEW (7.5mm) and 2.0ct DEW (8.0mm) are currently very popular in NZ. They offer a luxurious, eye-catching presence while remaining elegant and wearable for everyday use.
Does moissanite lose its sparkle over time?
No. Moissanite is a very hard gemstone (9.25 on the Mohs scale). It does not cloud or lose its brilliance over time. Regular cleaning with mild soap and water will keep it looking brand new.