How to assess diamond quality — 4Cs explained
When choosing a diamond, you'll inevitably encounter the term 4Cs. These are the four fundamental criteria by which gemologists worldwide evaluate diamond quality — and therefore price. The system was established by the Gemological Institute of America (GIA) in the 1950s and remains the standard today.
In this article we explain what each C means, how it affects appearance and value, and why one of them is by far the most important.
1. Carat — diamond mass
Carat (abbreviated ct) measures weight, not size. One carat equals 0.2 grams. A 1 ct diamond is approximately 6.5 mm in diameter (in round cut).
Price does not scale linearly: a 2-carat diamond is not twice as expensive — often four times. The reason is rarity — larger diamonds are exponentially harder to find.
Practical tip: A 0.90 ct diamond is visually almost identical to 1.00 ct but can save 20–30 % in price. Sizes "just below the magic threshold" are smart choices.
2. Cut — the most important C
Cut is the only one of the 4Cs that humans create. The others are nature-given. Cut quality determines how the diamond catches and reflects light — its brilliance.
Poor cut makes even a perfect gem dull. Excellent cut makes even a smaller diamond sparkle.
GIA cut grades:
- Excellent (5 % of all diamonds) — premium
- Very Good (15 %) — excellent choice
- Good (25 %) — good value, decent look
- Fair / Poor — we recommend against
The difference between Excellent and Good cut is visible at first glance. At Kraguljevich Jewelry we recommend Very Good minimum.
3. Color
Diamonds are graded on a D to Z scale:
- D, E, F — colorless (highest, most expensive)
- G, H, I — near colorless (excellent value)
- J, K — faintly yellow (visible to the eye)
- L+ — noticeably yellow
For custom jewelry we usually recommend G–I. The difference from D-F is almost imperceptible to an untrained eye but saves significantly.
Exception: fancy color diamonds (red, pink, blue, green) are a different story entirely — color is the highest value, not an imperfection.
4. Clarity
Under 10× magnification, gemologists look for internal inclusions and external blemishes. Scale:
- FL / IF — Flawless / Internally Flawless (very rare)
- VVS1, VVS2 — Very Very Slightly Included
- VS1, VS2 — Very Slightly Included
- SI1, SI2 — Slightly Included (visible under magnification)
- I1, I2, I3 — Included (visible to naked eye)
For custom jewelry VS1–VS2 is an excellent compromise. Inclusions are only under 10× magnification — invisible to the naked eye.
Which combination to choose?
There's no universal answer. Our recommendations for an engagement ring:
- Cut: Excellent or Very Good (never compromise)
- Color: G or H
- Clarity: VS1 or VS2
- Carat: what budget allows, preferably slightly less but better cut/color
Most important: rather 0.9 ct Excellent VS1 G than 1.2 ct Good SI2 J. The diamond will look more beautiful and brighter.
What's next?
All our diamond jewelry comes with a certificate including exact 4C data and stone description. Every piece can be verified.
Or contact us for a personal consultation — we'll help you choose the right diamond for your budget.
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Author: Kraguljevich Jewelry · Buyer's guide