Diamond Size Chart & MM to Carat Weight Calculator
Estimate a diamond's approximate carat weight from its millimeter measurements, compare common diamond sizes, and explore typical dimensions for the most popular diamond shapes.
Diamond carat and diamond size are not the same thing. Carat measures weight, while millimeters describe a diamond's physical dimensions. Two diamonds with the same carat weight can therefore look noticeably different depending on their shape, depth, proportions, and cutting style.
Diamond MM to Carat Weight Calculator
If you already have a diamond and know its measurements, use this calculator to estimate its approximate carat weight. Measurements are normally shown in millimeters on a diamond grading report.
If you do not know the depth—common with mounted diamonds—the calculator will use a typical reference depth for that shape. The resulting estimate will be less precise.
Do You Already Own This Diamond?
If you're using the calculator because you own, inherited, or are considering selling a diamond, approximate carat weight is only the beginning. For a natural diamond, cut, color, clarity, certification, condition, overall make, and current market demand can all have a major effect on value.
What brings you here?
Carat Weight to Typical Diamond Dimensions
Already know the carat weight? Use this calculator to see the approximate dimensions of a normally proportioned diamond of that shape.
Compare Diamond Sizes Side by Side
Carat weight does not always correspond directly to face-up appearance. Compare two diamond shapes and carat weights to see how their typical dimensions may differ.
The comparison is relative rather than a physically exact on-screen millimeter representation. Monitor size, browser zoom, and device resolution vary.
Diamond Size Charts by Shape
The charts below provide approximate reference dimensions for commonly proportioned diamonds. Actual dimensions vary, especially among fancy shapes where length-to-width ratio, depth, and cutting style can differ considerably.
Round Diamond Size Chart
| Carat Weight | Approx. Dimensions |
|---|---|
| 0.25 ct | 4.1 × 4.1 mm |
| 0.50 ct | 5.1 × 5.1 mm |
| 0.75 ct | 5.8 × 5.8 mm |
| 1.00 ct | 6.4 × 6.4 mm |
| 1.25 ct | 6.9 × 6.9 mm |
| 1.50 ct | 7.4 × 7.4 mm |
| 2.00 ct | 8.1 × 8.1 mm |
| 2.50 ct | 8.7 × 8.7 mm |
| 3.00 ct | 9.3 × 9.3 mm |
| 4.00 ct | 10.2 × 10.2 mm |
| 5.00 ct | 11.0 × 11.0 mm |
Oval Diamond Size Chart
| Carat Weight | Approx. Length × Width |
|---|---|
| 0.25 ct | 5.1 × 3.5 mm |
| 0.50 ct | 6.4 × 4.4 mm |
| 0.75 ct | 7.4 × 5.1 mm |
| 1.00 ct | 8.1 × 5.6 mm |
| 1.25 ct | 8.7 × 6.0 mm |
| 1.50 ct | 9.3 × 6.4 mm |
| 2.00 ct | 10.2 × 7.0 mm |
| 2.50 ct | 11.0 × 7.6 mm |
| 3.00 ct | 11.7 × 8.0 mm |
| 4.00 ct | 12.8 × 8.9 mm |
| 5.00 ct | 13.8 × 9.5 mm |
Cushion Diamond Size Chart
| Carat Weight | Approx. Length × Width |
|---|---|
| 0.25 ct | 3.7 × 3.5 mm |
| 0.50 ct | 4.7 × 4.4 mm |
| 0.75 ct | 5.3 × 5.1 mm |
| 1.00 ct | 5.9 × 5.6 mm |
| 1.25 ct | 6.3 × 6.0 mm |
| 1.50 ct | 6.7 × 6.4 mm |
| 2.00 ct | 7.4 × 7.0 mm |
| 2.50 ct | 8.0 × 7.6 mm |
| 3.00 ct | 8.5 × 8.1 mm |
| 4.00 ct | 9.3 × 8.9 mm |
| 5.00 ct | 10.0 × 9.6 mm |
Emerald-Cut Diamond Size Chart
| Carat Weight | Approx. Length × Width |
|---|---|
| 0.25 ct | 4.3 × 3.1 mm |
| 0.50 ct | 5.5 × 3.9 mm |
| 0.75 ct | 6.2 × 4.5 mm |
| 1.00 ct | 6.9 × 4.9 mm |
| 1.25 ct | 7.4 × 5.3 mm |
| 1.50 ct | 7.9 × 5.6 mm |
| 2.00 ct | 8.7 × 6.2 mm |
| 2.50 ct | 9.3 × 6.7 mm |
| 3.00 ct | 9.9 × 7.1 mm |
| 4.00 ct | 10.9 × 7.8 mm |
| 5.00 ct | 11.8 × 8.4 mm |
Radiant Diamond Size Chart
| Carat Weight | Approx. Length × Width |
|---|---|
| 0.25 ct | 4.3 × 3.2 mm |
| 0.50 ct | 5.5 × 4.1 mm |
| 0.75 ct | 6.3 × 4.6 mm |
| 1.00 ct | 6.9 × 5.1 mm |
| 1.25 ct | 7.4 × 5.5 mm |
| 1.50 ct | 7.9 × 5.8 mm |
| 2.00 ct | 8.7 × 6.4 mm |
| 2.50 ct | 9.4 × 6.9 mm |
| 3.00 ct | 9.9 × 7.4 mm |
| 4.00 ct | 10.9 × 8.1 mm |
| 5.00 ct | 11.8 × 8.7 mm |
Pear Diamond Size Chart
| Carat Weight | Approx. Length × Width |
|---|---|
| 0.25 ct | 5.5 × 3.5 mm |
| 0.50 ct | 6.9 × 4.4 mm |
| 0.75 ct | 7.9 × 5.1 mm |
| 1.00 ct | 8.7 × 5.6 mm |
| 1.25 ct | 9.3 × 6.0 mm |
| 1.50 ct | 9.9 × 6.4 mm |
| 2.00 ct | 10.9 × 7.0 mm |
| 2.50 ct | 11.8 × 7.6 mm |
| 3.00 ct | 12.5 × 8.1 mm |
| 4.00 ct | 13.8 × 8.9 mm |
| 5.00 ct | 14.8 × 9.6 mm |
Marquise Diamond Size Chart
| Carat Weight | Approx. Length × Width |
|---|---|
| 0.25 ct | 6.3 × 3.3 mm |
| 0.50 ct | 7.9 × 4.2 mm |
| 0.75 ct | 9.1 × 4.8 mm |
| 1.00 ct | 10.0 × 5.3 mm |
| 1.25 ct | 10.8 × 5.7 mm |
| 1.50 ct | 11.5 × 6.0 mm |
| 2.00 ct | 12.6 × 6.6 mm |
| 2.50 ct | 13.6 × 7.2 mm |
| 3.00 ct | 14.4 × 7.6 mm |
| 4.00 ct | 15.9 × 8.4 mm |
| 5.00 ct | 17.1 × 9.0 mm |
Princess-Cut Diamond Size Chart
| Carat Weight | Approx. Length × Width |
|---|---|
| 0.25 ct | 3.5 × 3.4 mm |
| 0.50 ct | 4.4 × 4.3 mm |
| 0.75 ct | 5.0 × 4.9 mm |
| 1.00 ct | 5.5 × 5.4 mm |
| 1.25 ct | 6.0 × 5.9 mm |
| 1.50 ct | 6.3 × 6.2 mm |
| 2.00 ct | 7.0 × 6.8 mm |
| 2.50 ct | 7.5 × 7.4 mm |
| 3.00 ct | 8.0 × 7.8 mm |
| 4.00 ct | 8.8 × 8.6 mm |
| 5.00 ct | 9.5 × 9.3 mm |
Asscher Diamond Size Chart
| Carat Weight | Approx. Dimensions |
|---|---|
| 0.25 ct | 3.6 × 3.6 mm |
| 0.50 ct | 4.5 × 4.5 mm |
| 0.75 ct | 5.2 × 5.2 mm |
| 1.00 ct | 5.7 × 5.7 mm |
| 1.25 ct | 6.1 × 6.1 mm |
| 1.50 ct | 6.5 × 6.5 mm |
| 2.00 ct | 7.2 × 7.2 mm |
| 2.50 ct | 7.7 × 7.7 mm |
| 3.00 ct | 8.2 × 8.2 mm |
| 4.00 ct | 9.0 × 9.0 mm |
| 5.00 ct | 9.7 × 9.7 mm |
Heart-Shaped Diamond Size Chart
| Carat Weight | Approx. Length × Width |
|---|---|
| 0.25 ct | 4.1 × 4.1 mm |
| 0.50 ct | 5.2 × 5.2 mm |
| 0.75 ct | 5.9 × 5.9 mm |
| 1.00 ct | 6.5 × 6.5 mm |
| 1.25 ct | 7.0 × 7.0 mm |
| 1.50 ct | 7.4 × 7.4 mm |
| 2.00 ct | 8.2 × 8.2 mm |
| 2.50 ct | 8.8 × 8.8 mm |
| 3.00 ct | 9.4 × 9.4 mm |
| 4.00 ct | 10.3 × 10.3 mm |
| 5.00 ct | 11.1 × 11.1 mm |
How to Estimate the Carat Weight of a Mounted Diamond
Mounted diamonds can be difficult to weigh because the stone cannot simply be placed on a diamond scale. Instead, jewelers can measure the stone's visible dimensions and use those measurements to produce an approximate weight.
For a round brilliant diamond, the estimate uses the average diameter and depth. Fancy shapes require length, width, depth, and a shape-specific adjustment factor.
If the depth cannot be measured because the diamond is mounted, the result becomes less precise. Our calculator can substitute a typical reference depth, but the result should always be treated as an approximation.
You don't need to remove the stone yourself. If you're considering selling a natural diamond or inherited diamond ring, Joseph Diamonds can evaluate the mounted diamond along with the setting, natural accent diamonds, precious metal, and any designer or estate characteristics.
Send Photos for a Quote
Why Two Diamonds With the Same Carat Weight Can Look Different
Carat weight measures how much a diamond weighs—not how large it looks from the top.
A deeper diamond can carry more of its weight below the girdle, while another diamond of the same weight may distribute more of its weight across its face-up surface. Diamond shape also has a significant effect on apparent size.
This is why a 2.00-carat oval, marquise, emerald cut, cushion, and round diamond can all have noticeably different face-up dimensions even though they weigh the same.
Does a Larger-Looking Diamond Mean It Is Worth More?
No. Face-up size is only one characteristic of a diamond.
Professional buyers evaluating natural diamonds may also consider:
- Carat weight
- Cut quality
- Color
- Clarity
- Shape
- Proportions
- Overall make and eye appeal
- Fluorescence
- Laboratory certification
- Current market demand
Two natural diamonds with similar dimensions can therefore have dramatically different market values.
For a deeper explanation, read Why Some Diamond Rings Are Worth Thousands More Than Others.
Natural vs. Lab-Grown Diamonds
Millimeter dimensions cannot determine whether a diamond is natural or laboratory-grown. Natural and lab-grown diamonds can have similar shapes, dimensions, and visual characteristics.
Diamond origin must be determined separately through documentation, professional screening, or appropriate gemological testing.
Learn more in Natural vs. Lab-Grown Diamonds: What Every Diamond Owner Should Know Before Selling.
Have a Natural Diamond to Sell in Kansas City or Overland Park?
If you're using this diamond size calculator because you already own a natural diamond, its approximate carat weight is only one part of determining value.
Joseph Diamonds provides private natural diamond evaluations in Overland Park for clients throughout the Kansas City area. We purchase loose natural diamonds, diamond engagement rings, estate diamond jewelry, and other significant natural diamond pieces.
Learn About Selling a Natural Diamond Send Photos for a Quote Book a Private Appointment
Diamond Size & Carat Weight FAQ
How many carats is a 6.5 mm round diamond?
A normally proportioned round brilliant measuring approximately 6.4–6.5 mm in diameter is often close to 1.00 carat. Actual weight can vary depending on depth, girdle thickness, and proportions.
How many carats is an 8 mm round diamond?
A normally proportioned round diamond measuring around 8.0–8.2 mm in diameter is commonly near 2.00 carats, although actual weight can vary.
Can I calculate diamond carat weight from millimeters?
You can estimate it using the diamond's length, width, depth, shape, and an appropriate shape factor. Only weighing the loose diamond provides an exact carat weight.
Can I estimate the weight of a diamond while it is still in a ring?
Yes. An approximate weight can often be calculated from measurements. The estimate becomes less precise when the setting prevents an accurate depth measurement.
Why does my diamond look larger than another diamond with the same carat weight?
The stones may distribute their weight differently. Shape, depth, proportions, and cutting style all affect face-up appearance.
Which diamond shapes tend to look larger face-up?
Elongated shapes such as oval, pear, and marquise diamonds often provide greater apparent length for a given carat weight. However, proportions vary substantially from diamond to diamond.
Does diamond size tell me what my diamond is worth?
No. Carat weight and dimensions are only part of the valuation process. Cut, color, clarity, natural origin, certification, condition, and current market demand can all materially affect value.
About these estimates: Diamond carat weight is a measurement of weight, with one metric carat equal to 200 milligrams. Dimension-based calculations and size charts on this page are intended as educational estimates and reference points. Actual diamond dimensions and weights vary according to proportions and cutting style.