We analyzed the 70000+ engagement rings in James Allen’s diamond inspiration gallery to determine what size diamonds people buy in practice.
Natural Diamonds
The table below shows the carats for each percentile by diamond shape. For example, for round natural diamonds, the median carat weight (50th percentile) is 0.88ct, while the 75th percentile is 1.09ct.
| Shape | 5% | 10% | 25% | 50% | 75% | 90% | 95% |
|---|---|---|---|---|---|---|---|
| Round | 0.41 | 0.5 | 0.7 | 0.88 | 1.09 | 1.5 | 1.74 |
| Cushion | 0.52 | 0.7 | 0.85 | 1.01 | 1.21 | 1.7 | 2.01 |
| Radiant | 0.51 | 0.64 | 0.81 | 1.01 | 1.3 | 1.76 | 2.02 |
| Princess | 0.45 | 0.51 | 0.71 | 0.92 | 1.05 | 1.5 | 1.71 |
| Oval | 0.5 | 0.6 | 0.76 | 1 | 1.15 | 1.51 | 1.8 |
| Pear | 0.5 | 0.51 | 0.71 | 0.9 | 1.03 | 1.32 | 1.51 |
| Marquise | 0.43 | 0.5 | 0.61 | 0.77 | 1 | 1.11 | 1.22 |
| Heart | 0.42 | 0.5 | 0.7 | 0.82 | 1.01 | 1.15 | 1.51 |
| Emerald | 0.51 | 0.69 | 0.82 | 1.01 | 1.32 | 1.74 | 2.02 |
| Asscher | 0.7 | 0.7 | 0.84 | 1.01 | 1.2 | 1.6 | 2 |
The table below summarizes the data from the other direction – what is the percentile for milestone carat weights? For example, for round natural diamonds, a 1ct diamond is the 66th percentile and a 1.5ct diamond is the 90th percentile.
| Shape | 0.25ct | 0.5ct | 0.75ct | 1ct | 1.25ct | 1.5ct | 1.75ct | 2ct | 2.25ct | 2.5ct |
|---|---|---|---|---|---|---|---|---|---|---|
| Round | 0.01 | 0.13 | 0.38 | 0.66 | 0.82 | 0.9 | 0.95 | 0.97 | 0.99 | 0.99 |
| Cushion | 0 | 0.03 | 0.17 | 0.46 | 0.78 | 0.86 | 0.92 | 0.95 | 0.99 | 0.99 |
| Radiant | 0 | 0.05 | 0.21 | 0.42 | 0.72 | 0.83 | 0.9 | 0.93 | 0.98 | 0.98 |
| Princess | 0 | 0.09 | 0.32 | 0.6 | 0.85 | 0.91 | 0.96 | 0.97 | 0.99 | 0.99 |
| Oval | 0 | 0.05 | 0.25 | 0.55 | 0.82 | 0.88 | 0.95 | 0.97 | 0.99 | 0.99 |
| Pear | 0 | 0.08 | 0.33 | 0.64 | 0.88 | 0.94 | 0.97 | 0.98 | 1 | 1 |
| Marquise | 0 | 0.14 | 0.49 | 0.76 | 0.96 | 0.97 | 0.99 | 1 | 1 | 1 |
| Heart | 0 | 0.13 | 0.39 | 0.74 | 0.92 | 0.94 | 0.98 | 0.99 | 1 | 1 |
| Emerald | 0 | 0.04 | 0.19 | 0.46 | 0.71 | 0.82 | 0.9 | 0.93 | 0.98 | 0.98 |
| Asscher | 0 | 0.01 | 0.19 | 0.44 | 0.78 | 0.85 | 0.93 | 0.96 | 0.99 | 0.99 |
Tables are easy to understand, but provide a limited summary of the data. The empirical cumulative distribution function of natural diamond carat weight is shown below. You can estimate the percentile for any carat weight from these graphs.
Lab-Created Diamonds
The table below shows the carats for each percentile by diamond shape. For example, for round lab diamonds, the median carat weight (50th percentile) is 1.13ct, while the 75th percentile is 1.36ct. The carat weights for lab diamonds are higher than for natural diamonds – people are buying larger lab diamonds due to their lower prices.
| Shape | 5% | 10% | 25% | 50% | 75% | 90% | 95% |
|---|---|---|---|---|---|---|---|
| Round | 0.71 | 0.8 | 0.92 | 1.13 | 1.36 | 1.65 | 1.9 |
| Cushion | 0.93 | 0.97 | 1.01 | 1.01 | 1.1 | 1.48 | 2.06 |
| Radiant | 0.85 | 0.9 | 1.01 | 1.02 | 1.03 | 1.04 | 1.04 |
| Princess | 0.72 | 0.84 | 1.01 | 1.52 | 1.73 | 1.99 | 2.05 |
| Oval | 0.53 | 0.63 | 0.81 | 0.95 | 1.05 | 1.14 | 1.17 |
| Pear | 0.59 | 0.7 | 0.72 | 0.77 | 1.01 | 1.04 | 1.17 |
| Emerald | 0.79 | 0.82 | 1 | 1.05 | 1.5 | 1.53 | 1.56 |
| Asscher | 1.06 | 1.07 | 1.08 | 1.29 | 1.5 | 1.51 | 1.51 |
The table below summarizes the percentiles for milestone carat weights. For example, for round lab diamonds, a 1ct diamond is the 32nd percentile and a 1.5ct diamond is the 81st percentile.
| Shape | 0.25ct | 0.5ct | 0.75ct | 1ct | 1.25ct | 1.5ct | 1.75ct | 2ct | 2.25ct | 2.5ct |
|---|---|---|---|---|---|---|---|---|---|---|
| Round | 0 | 0 | 0.08 | 0.32 | 0.66 | 0.81 | 0.92 | 0.96 | 0.98 | 0.99 |
| Cushion | 0 | 0 | 0.05 | 0.24 | 0.88 | 0.88 | 0.93 | 0.93 | 1 | 1 |
| Radiant | 0 | 0 | 0 | 0.17 | 1 | 1 | 1 | 1 | 1 | 1 |
| Princess | 0 | 0 | 0.08 | 0.24 | 0.44 | 0.48 | 0.76 | 0.88 | 1 | 1 |
| Oval | 0 | 0.03 | 0.21 | 0.58 | 0.96 | 0.96 | 0.96 | 0.96 | 1 | 1 |
| Pear | 0 | 0.04 | 0.43 | 0.7 | 1 | 1 | 1 | 1 | 1 | 1 |
| Emerald | 0 | 0 | 0.04 | 0.26 | 0.72 | 0.74 | 1 | 1 | 1 | 1 |
| Asscher | 0 | 0 | 0 | 0 | 0.5 | 0.75 | 1 | 1 | 1 | 1 |
The full empirical cumulative distribution function of lab diamond carat weight is shown below. James Allen only started selling lab-created diamonds in the second half of 2019. The sample size of the fancy shaped diamonds is relatively small, leading to a more discontinuous CDF.
