What is the price and market value of a 1 carat diamond? How to buy high-quality loose items within your budget
💎 Diamond basic knowledge
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What is the size and price range?
Explaining how to choose without making mistakes
Weight: 0.2g, diameter: approx. 6.5mm --- The price for the same 1 carat item ranges from 200,000 to over 3,000,000 yen, depending on the quality (4C).
Selby, a jewelry specialty store in Okachimachi, will explain everything about how to choose.
6.5mm Diameter (round)
0.2g Weight = 1 carat
200,000 to over 3 million yen Price range (depending on 4C)
Last updated: Reflecting market information as of May 2026
Compare the coveted 1 carat diamonds at Selby
Even with the same 1 carat, the shine and price can vary greatly depending on the color, clarity, and cut. You can find a 1 carat diamond that matches your budget and preferences while comparing the balance between quality and price.
Compare 1ct
Choose from 4C
Check quality
First of all, what does "1 carat" mean? ─ Unit of “weight” rather than size
1 carat = 0.2g. The origin of the word is "locust bean"
"Carat/ct" isunit of weightSo,1 carat = 0.2 grams (200 milligrams)is internationally defined. The origin of the word comes from the ``carob bean'' that grows wild on the Mediterranean coast, and because its weight was almost constant, it was used by ancient jewelry merchants as a weight for balances.
Carat is often misunderstood as "size," but it is actually a unit of weight. Even with the same 1 carat, it varies depending on the shape and depth of the cut.The visible size changes。
Be careful not to confuse it with gold “Karat” The ``Carat (ct)'' of diamond is a unit of weight, and the ``Karat (K)'' of gold is a unit of purity. This is a different concept from the "K" in K18 and K24.
The diameter of 1 carat is approximately 6.5 mm -- about the same as the hole in a 5-yen coin.
For round brilliant cuts (the most common round cut for engagement rings), the approximate carat size is as follows:
💎 Diamond diameter comparison by carat (round brilliant cut)
0.2ct
Approximately 3.8mm
0.3ct
Approximately 4.3mm
0.5ct
Approximately 5.2mm
★ 1.0ct
Approximately 6.5mm
1.5ct
Approximately 7.4mm
2.0ct
Approximately 8.2mm
3.0ct
Approximately 9.4mm
5 yen coin hole
Diameter 5mm
＜
1 carat diamond
Diameter approximately 6.5mm
| carat | Diameter (approximate) | weight | impression of appearance |
|---|---|---|---|
| 0.2ct | Approximately 3.8mm | 0.04g | Moderate/daily use |
| 0.3ct | Approximately 4.3mm | 0.06g | Minimal engagement ring standard |
| 0.5ct | Approximately 5.2mm | 0.10g | A gorgeous presence in your hand |
| ★ 1.0ct | Approximately 6.5mm | 0.20g | Milestone size called "carat diamond" |
| 1.5ct | Approximately 7.4mm | 0.30g | A ring with a leading role |
| 2.0ct | Approximately 8.2mm | 0.40g | Party/souvenir class |
| 3.0ct | Approximately 9.4mm | 0.60g | Collector/Investment Class |
Tips for feeling The diameter of 1 carat is 6.5 mm, which is one size larger than the hole (5 mm) in a 5-yen coin. If you are having trouble getting an idea of the real thing, you can get a sense of it by holding a 5 yen coin against your finger.
Average price of 1 carat diamond ─ Range from 200,000 yen to over 3 million yen
Price is determined by "4C"
The price of a 1 carat diamond isNumber of carats, color, clarity, cutThe four elements of ── the so-called4CIt is determined by the combination of Even with the same 1 carat, the lowest class and the highest classPrice difference more than 10 timeswill appear.
💎 "4C" determines the quality of diamonds
carat
Carat
Weight (= approximate size)
color
Color
The closer it is to colorless, the higher the rating.
clarity
Clarity
Few inclusions
cut
Cut
Polishing technology that creates shine
1 carat price chart (with GIA certificate/reference price)
The following is a guideline range (tax included) observed in the secondary market. It varies depending on the market price. The latest stock price is Selby diamond loose list Please check.
*Cut grade is assumed to be 3EX (triple excellent). Fair/Poor tends to fall further by 10-30%.
*Cut grade is assumed to be 3EX (triple excellent). Fair/Poor tends to fall further by 10-30%.
| Color ＼ Clarity | IF~VVS1 | VVS2～VS1 | VS2~SI1 | SI2 |
|---|---|---|---|---|
| D~F (colorless) | 2.2 million to 1.5 million yen | 1.5 million to 1 million yen | 1 million to 600,000 yen | 600,000 to 300,000 yen |
| G~H (almost colorless) | 1.5 million to 1 million yen | 1 million to 700,000 yen | 700,000 to 500,000 yen | 500,000 to 250,000 yen |
| I~J (slight color) | 800,000 to 600,000 yen | 600,000 to 500,000 yen | 500,000 to 350,000 yen | 350,000 to 200,000 yen |
| K~M (light yellowish) | 500,000 to 400,000 yen | 400,000 to 300,000 yen | 300,000 to 200,000 yen | ~200,000 yen |
📊 1 carat diamond price range map (by 4C grade)
Market trends in 2026 ─ “Selector advantage” phase
It is the world diamond wholesale price index.Rapaport1ct RAPI index for the full year 2025Approximately -9.9%And the downward trend continues. Even after entering 2026, there will be limited movement towards bottoming out.It is easy for buyers and selectors to make careful comparisons.It is.
📉 1 carat diamond price trend image (RAPI index base)
market points Now that prices are calm, it's better to make a hasty decision.Timing when you can aim for “one-grade higher quality with the same budget”I can say that. For details on market trends, Diamond monthly market report Please refer to
Compare the coveted 1 carat diamonds at Selby
Even with the same 1 carat, the shine and price can vary greatly depending on the color, clarity, and cut. You can find a 1 carat diamond that matches your budget and preferences while comparing the balance between quality and price.
Compare 1ct
Choose from 4C
Check quality
4 steps to choose 1 carat without failure
1
Decide on “1C to focus on”
If all 4Cs are given the highest rating, the price will skyrocket. First of allWhat do you value most?Let's decide.
| Important points | Priority 4C | For people like this |
|---|---|---|
| Presence and size | carat | Engagement ring with emphasis on volume |
| Transparency/cleanliness | clarity | Those looking for an elegant impression |
| brilliant shine | cut | Emphasis on photogenicity and sparkle |
| Peace of mind/future resale | Certificate of authenticity (GIA, etc.) | First big purchase |
2
Be sure to select “With certificate of authenticity”
In the 1 carat band,Comes with a GIA or CGL (Central Gem Laboratory) certificate of authenticityThe golden rule is to choose. Also note the year of issue of the certificate. C.G.L.Current standards since 2014is recommended. For more details Differences between GIA and Central Gem Laboratory (CGL) | Risks of old certificates Please also check.
3
See and compare the real thing
Even if the numbers are the same, the actual shine and transparency will differ from stone to stone. In a jewelry town like OkachimachiCompare multiple routes side by sideThe biggest trick to not failing is to take advantage of the environment where you can.
4
Focusing on tailoring (rings and pendants)
The appropriate carat and shape will vary depending on whether you want to keep only a loose piece, make it into an engagement ring, or make it into a pendant. Options for fancy cuts (other than round) Types of fancy cut diamonds and how to choose them Please refer to
🔄 How to choose without failure
⚠️ Common mistakes ─ 5 ways to regret choosing 1 carat
Introducing patterns of ``regrets after purchasing'' that we often hear from customers.
❌ ① Make a decision based only on “numbers” and regret it when the real thing shines
Items with a cut rating of "Good" or lower have significantly lower shine even if the color and clarity are the same.Don't compromise on the cutis the golden rule.
❌ ② The appraisal was a “CGL old appraisal from 2014 or earlier”
CGL revised its appraisal standards in 2014, and the grade of the old appraisal isIf reappraised using current standards, color and clarity may drop by one rank.There is. Be especially careful with second-hand market and auction items.
❌ ③ Fluorescence “Strong / Very Strong” makes it cloudy
Fluorescence itself is not a drawback, but if it is strong or higher and is described as "milky", the shine may appear dull.Be sure to check the fluorescence items with the certificate of authenticity.Let's do it.
❌ ④ I chose a deep cut to “gain more carats”
Even with the same 1.0ct, stones with larger depth areSmall diameter when viewed from the frontI can see it. Be careful with 1ct stones that are "less than 6.5mm".
❌ ⑤ Purchase "without certificate" at a non-brand store
Although the price is attractive, the futureSignificant reduction when purchasing or resaleIt's easy to get sick, and you can't get insurance. This is a particularly risky choice for the 1ct band.
The biggest point to prevent failure Of the 5 patterns above, ①②③ areHow to read a certificateYou can avoid it just by knowing.Difference between GIA and CGLWe strongly recommend that you understand this in advance.
By scenario - How to choose the best 1 carat for you
Scene 1: Giving as an engagement ring
A classic combination that provides both peace of mind and beauty. Selecting platinum/K18 base metal according to the thickness and design of your fingers will improve the quality of your look.
D~F/VVS~VS/3EX/Fluorescence None~Faint/GIA certificate included
Estimated budget: 1.8 million to 2.6 million yen
Scene 2: Souvenirs/rewards for yourself
There is almost no difference to the naked eye, and the gorgeous appearance is comparable to the classic specs. Best-in-class combination for cost performance.
G~H/VS2~SI1/3EX
Estimated budget: 800,000 to 1,400,000 yen
Scene 3: One stone with asset value in mind
A combination that is likely to be evaluated at future resales. Also consider type IIa (a rare classification with extremely low nitrogen impurities).
D~E / VVS1 or higher / 3EX / Fluorescence None / GIA certificate included
Estimated budget: 2 million yen ~
Scene 4: Live commerce/liver purchasing
Reliability is greatly improved because the identification number can be presented to the viewer during the broadcast. Selby is used by many as a procurement location for inquiries and livers via SNS.
Comes with GIA certificate / laser engraved
Consultation depending on purchasing band
Compare the coveted 1 carat diamonds at Selby
Even with the same 1 carat, the shine and price can vary greatly depending on the color, clarity, and cut. You can find a 1 carat diamond that matches your budget and preferences while comparing the balance between quality and price.
Compare 1ct
Choose from 4C
Check quality
Benefits of choosing a 1 carat loose diamond from Selby
1
``Comparison possible'' with monthly listing volume of 2,500 to 3,000 items
With over 20 years of sales experience and a monthly listing volume of 2,500 to 3,000 items, you can compare multiple loose 1 carat belts side by side.
2
Mainly GIA, only current certificates are used.
Only GIA/CGL current certificates are used for new products (first hand diamonds). The risk of old appraisals is structurally eliminated.
3
Reduce intermediate costs with first-hand diamonds
By purchasing directly from our long-standing overseas network, we are able to offer prices that do not include intermediate costs associated with auctions.
4
Actual comparison available at 2 Okachimachi stores
You can visit our 2 stores, Okachimachi Main Store and Okachimachi Ekimae Store, to check out the loose items you are interested in online.
5
Komehei Group's only jewelry specialty company
Under the umbrella of Komehyo Holdings, which is listed on the Tokyo Stock Exchange Standard and Nagoya Stock Exchange Main, we have a management system that specializes in jewelry. We can handle everything from post-purchase consultation to purchase and storage.
❓ Frequently asked questions (FAQ)
With round brilliant cutApproximately 6.5mm in diameter, 0.2g in weightIt is. It is one size larger than the hole (5mm) on a 5 yen coin.
With classic specs (D~F/VVS~VS/3EX/GIA)1.8 million to 2.6 million yen, in cost performance class (G~H/VS2~SI1)800,000 to 1,400,000 yenis the standard.
The physical and chemical properties are the same as natural ones, but the price isAbout 1/5 to 1/10 of naturalIt is. On the other hand, in the resale market, valuations tend to drop significantly, so if you are conscious of long-term holding and asset quality,naturalis recommended.
The 1ct RAPI index in 2025 isDeclining trend of approximately -9.9%This is an easy situation to compare and consider. There is no need to make a hasty decision, and this is a good time to carefully compare multiple stones.
Wholesale, retail, and processing are all concentrated within walking distance.Japan's largest jewelry streetThe biggest advantage is that it is easy to compare multiple stores side by side. For more details Advantages of finding loose diamonds in Okachimachi Please take a look.
There is no problem as long as it comes with a GIA certificate and is managed by a clear company. Selby isBoth EC + physical storeNarrow down your choices online and then visit the store for final confirmation.hybrid purchaseis possible.
💎 Summary: ``1 carat'' is determined not by the number, but by the way you choose it.
1 carat diamond isApproximately 6.5mm in diameter, 0.2g in weightWhile the physical definition remains the same, it depends on the combination of the 4Cs.200,000 yen to over 3 million yenand prices vary widely.
✅ 4 points to avoid failure
- 1C to focus onDeciding on (carat/color/clarity/cut) first
- Comes with GIA or CGL current certificateto choose
- An environment where you can compare multiple real itemsto consider in
- Considering the tailoring and future usagechoosing
By keeping these four points in mind, you can greatly reduce the regrets that ``it wasn't what I expected.''
As the Komehei Group's only jewelry specialty company, Selby operates both at its store in Okachimachi and on the e-commerce site.1 carat ideal stoneWe will help you meet.
Compare the coveted 1 carat diamonds at Selby
Even with the same 1 carat, the shine and price can vary greatly depending on the color, clarity, and cut. You can find a 1 carat diamond that matches your budget and preferences while comparing the balance between quality and price.
Compare 1ct
Choose from 4C
Check quality