Moissanite and Diamond Size Comparison Chart

Choosing between moissanite and a lab grown diamond often comes down to one practical question: how big will it actually look on your hand? Carat weight alone doesn’t answer this — moissanite is less dense than diamond, so a moissanite stone of the same carat weight measures slightly larger across. This chart compares both by millimeter size, the measurement that actually determines how a stone looks set in a ring.

Why Moissanite Looks Slightly Larger

Moissanite has a lower density than diamond — roughly 3.21 g/cm³ versus diamond’s 3.52 g/cm³. That means for the same physical width, moissanite weighs less. In practice, a moissanite stone cut to the same millimeter size as a 1-carat diamond will typically weigh around 0.85-0.90 carats — but it will look the same size on your finger, because size as seen by the eye is determined by the stone’s diameter, not its weight. This is why we always recommend choosing by millimeter measurement rather than carat weight alone when comparing the two

How to Use This Chart

Find the shape you’re considering, then match it to the size you want — either by carat (if you’re set on a specific diamond weight) or by millimeter (if you’re matching an existing setting or comparing against a piece you’ve seen in person). For custom orders, both lab grown diamonds and moissanite are available across all shapes and sizes shown here, plus specialty cuts on request — sourced and verified within 2 hours through our Surat network if not currently in stock. [Browse lab grown diamonds →] [Browse moissanite stones →]