The 5th C, Our Caratlytics
Every diamond gets a grade from A+ to D. Here's how we calculate it and what the grades mean.
What is the 5th C?
You already know the 4Cs: Cut, Color, Clarity, and Carat. They describe a diamond's gemological properties. But they don't tell you whether you're getting a good deal, whether the certification is trustworthy, or how the price compares to the same stone at another retailer.
Our Caratlytics is the 5th C. It combines quality, value, certification, and market data into a single letter grade from A+ to D. Think of it as an overall grade for the entire listing, not just the stone, but the deal.
The same physical diamond can have different grades at different retailers. A 1.50ct Round with GIA certification might get an A at one store and a B+ at another if the second retailer charges 30% more for the same stone.
Grade Scale
Every diamond listing gets a letter grade so you can quickly gauge quality at a glance.
Sub-Scores Explained
The overall score is a weighted average of four sub-scores. Each measures a different dimension of what makes a diamond listing worth buying.
Quality
35%Gemological perfection. How well-cut, well-graded, and well-proportioned is this diamond?
- ·Cut, polish, and symmetry grades
- ·Table and depth percentages vs. ideal ranges
- ·Color and clarity relative to category peers
- ·Fluorescence impact on appearance
Value
30%Bang for your buck. How does this diamond's price compare to similar stones across retailers?
- ·Price percentile within category (origin + shape + carat range)
- ·Carat threshold positioning (e.g. 0.99ct vs 1.00ct)
- ·Cross retailer price position (cheapest, mid range, or most expensive)
- ·Price to specification ratio
Certification
20%Trustworthiness. Can you independently verify that this diamond is what the seller claims?
- ·Lab reputation (GIA, IGI, HRD, GCAL, AGS, etc.)
- ·Data completeness: are all key specs reported?
- ·Certificate availability (can you check it yourself?)
- ·Presence of measurements and proportions
Market
15%Price intelligence. How much market data do we have to validate this diamond's pricing?
- ·Cross retailer verification (same stone at multiple stores)
- ·Active listing count for this certificate
- ·Price trend stability over time
- ·Retailer reputation and track record
Category Percentile
On each diamond's detail page you'll see something like "Top 12% of Lab Grown Round 1.00-1.49ct diamonds". This is the category percentile: how this listing ranks against all other diamonds with the same origin, shape, and carat range.
We group diamonds into categories because it doesn't make sense to compare a 0.50ct lab grown to a 3.00ct natural. The percentile tells you how competitive this specific listing is among its true peers.
A diamond can have a B+ grade but still rank in the top 5% of its category if most diamonds in that carat range are priced much higher. The percentile is relative to the competition, not absolute.
How to Use It
The score is a starting point, not the final word. Here's how to get the most from it:
Use the "Best Grade" sort in search to surface the best overall deals. Filter by "B+ and above" to skip the noise.
Compare grades within the same specs. Two 1.00ct G VS2 Rounds graded A and B? The first is likely better priced at a more reputable store.
Check the sub-score breakdown. A high Value score with a lower Quality score means you're getting a bargain on a less-perfect stone, which might be exactly what you want.
Look at the category percentile. "Top 8%" means you're near the best deal available for that type of diamond right now.
Always inspect the actual specs. The grade helps you shortlist, but your eyes and priorities make the final call.
Grades are recalculated daily as prices change and new listings appear. A diamond graded B+ today might move to A tomorrow if a more expensive listing at another retailer is removed, shifting the price percentile.