What the score is
We built the Diamond Watcher Score because sorting a few hundred stones from Blue Nile, Ritani, Rare Carat and the rest by price alone tells you almost nothing. Every listing in search gets one. Cut, color and clarity carry the most weight, the grading lab comes next, and price per carat and the return window round it out.
Use it to cut the list down. It's good at pushing poorly cut or weakly graded listings to the bottom, and the breakdown shows which factors helped and which held a stone back. The final call still needs your eyes on a photo or video.
Where the points come from
The 4Cs make up about half the score, and cut carries the most weight on its own, because it does more for sparkle than any other grade. These are the main inputs. The exact weights and adjustments are ours, and we tune them as we learn what makes a good buy.
- Cut
- Carat
- Color
- Clarity
- Certificate lab
- Polish & symmetry
- Fluorescence
- Price per carat
- Video
- Photos
- Return policy
- Shape proportions
| Factor | What scores well |
|---|---|
| Cut | The biggest single factor. Excellent and Ideal score highest, and each step down costs more than a step down in any other grade. |
| Carat | Bigger scores higher, but the scale runs well past engagement sizes, so similar-sized stones land close together. |
| Color | Colorless scores highest. Each grade down costs a little, so the near-colorless range (G to J) stays competitive. |
| Clarity | Eases down gently through the VS grades, then drops more sharply at SI and below. |
| Certificate lab | GIA scores highest, then AGS, then IGI. Other labs earn less or nothing. |
| Polish & symmetry | Rewards Excellent or Very Good polish and symmetry. |
| Fluorescence | None or faint is best. Strong fluorescence costs points. |
| Price per carat | Lower price per carat helps, but it's measured on a broad scale, so similar listings barely differ on it. |
| Video | Listings with a 360° video get credit. |
| Photos | Listings with real photos get credit. |
| Return policy | Longer return windows score higher. |
| Shape proportions | L/W ratio, depth %, table % and face-up spread, checked against the ideal range for the shape. Capped so proportions never outweigh the 4Cs. |
Price per carat is measured on a broad fixed scale, not against similar stones, so two listings with the same specs end up nearly level on it even when one costs far more. Treat the score as a read on quality, and do the price comparison yourself by lining up the same specs across retailers.
Which grades matter most
A step down in grade doesn't cost the same everywhere. Dropping one cut grade costs several times what dropping one color grade does, which is a decent hint about where to spend.
- Color costs a little per grade, so the near-colorless range (G to J) stays close to the top.
- Clarity eases down through the VS grades, then drops harder at SI1 and again at I1.
- Cut has the steepest steps. A Good cut is a real handicap before anything else is counted.
- The lab matters too: GIA scores highest, then AGS, then IGI.
Shape and proportions
Grades alone don't tell you if a stone is well proportioned, so the score also checks four measurements against the ideal range for its shape: length-to-width ratio, depth %, table % and face-up spread (how much surface area you get per carat). Proportions are capped, so a nicely proportioned stone gets credit without proportions drowning out the 4Cs.
| Shape | Ideal L/W ratio | Ideal depth % | Ideal table % |
|---|---|---|---|
| Round | 0.99 to 1.01 | 59 to 63% | 54 to 58% |
| Princess | 0.98 to 1.02 | 68 to 75% | 65 to 75% |
| Emerald | 1.30 to 1.50 | 60 to 70% | 60 to 70% |
| Cushion | 1.00 to 1.10 | 61 to 68% | 60 to 70% |
| Asscher | 0.98 to 1.02 | 60 to 68% | 60 to 68% |
| Oval | 1.30 to 1.50 | 58 to 62% | 53 to 63% |
If you're torn between shapes, our diamond size chart shows how big each one looks at the same carat weight.
A worked example
Here's a typical engagement-ring stone run through the same scoring code our search uses: a 1.00 carat round, G color, VS1 clarity, Excellent cut, graded by GIA with faint fluorescence, priced at $6,800, with a video, photos and a 30-day return window.
Most of the meters are full or close to it, yet it lands at 8.18. Carat is most of the gap, because the size scale runs well past engagement sizes. Put it next to other 1 carat stones and that handicap washes out, since they all carry it.
Try it on a diamond
Plug in a stone you're considering, or change one grade at a time to see how it moves the score. It runs the same scoring our search uses.
Using the score when you shop
- Search with your must-haves. Set shape, carat range and budget in diamond search first, so you're only ranking stones you'd actually buy.
- Sort by Score. Click the Score column header to bring the strongest listings to the top.
- Hover over a score. The breakdown shows which factors earned points and which didn't.
- Compare close calls on price yourself. The score hardly reacts to price, so when two stones are within a few tenths, check which is cheaper and which has the longer return window.
What the score can't see
- Where an inclusion sits. Two VS2 stones score the same even if one has a dark crystal under the table.
- Light performance beyond the grades: no ASET or Hearts and Arrows images go into it.
- Whether a stone's fluorescence actually makes it look hazy, which only a photo or video can show you.
- Your own priorities. If you care most about size, a lower-scoring larger stone can still be the right pick.