IGI and GIA are both legitimate gemmological laboratories, and neither one makes a diamond better. IGI grades the large majority of the world's lab-grown diamonds and issues a full 4C report with a laser-inscribed number on the stone. GIA reports on lab-grown diamonds are less common and usually cost more. For a lab-grown diamond, IGI is the practical standard.
What is the difference between IGI and GIA?
GIA (Gemological Institute of America) was founded in 1931 and invented the 4Cs: carat, colour, clarity and cut. Every grading vocabulary you have ever read on a jewellery website traces back to that system. GIA built its reputation on natural diamonds, and for years it deliberately kept lab-grown reports simple and descriptive rather than issuing the same full grades it gave natural stones. It has since moved to full 4C-style grading for lab-grown diamonds.
IGI (International Gemological Institute) was founded in 1975 in Antwerp, the historic centre of the diamond trade. When lab-grown diamonds started to scale, IGI moved first and built the capacity to grade them at volume. That head start is why almost every lab-grown stone you see quoted with a report number today is quoted with an IGI number.
So the honest answer to "which is stricter" is: they are different houses with slightly different grading tolerances, and any two labs will occasionally disagree by one grade on a borderline stone. That is true of natural diamonds too. It is not evidence of fraud, and you should be sceptical of any seller who tells you a rival lab is fake.
Which lab grades most lab-grown diamonds?
IGI, by a wide margin. If you are shopping for a lab-grown diamond in Hong Kong, Singapore or Taipei, the stone in front of you was almost certainly graded by IGI, because that is what the lab-grown supply chain runs on. Insisting on a GIA report for a lab-grown stone is possible, but it narrows your choice and it costs more, and the report will tell you roughly the same thing about the same stone.
IGI vs GIA at a glance
| IGI | GIA | |
|---|---|---|
| Founded | 1975, Antwerp | 1931, United States |
| What it grades | Natural and lab-grown diamonds, coloured stones, finished jewellery | Natural and lab-grown diamonds, coloured stones; creator of the 4Cs |
| Coverage of lab-grown | Grades most of the world's lab-grown diamonds | Present but far less common in the lab-grown supply chain |
| What the report contains | Full 4Cs, measurements, proportions, fluorescence, growth method, plotted comments | Full 4C-style grading for lab-grown, plus identification as laboratory-grown |
| Laser inscription | Report number inscribed on the girdle, verifiable online | Report number inscribed on the girdle, verifiable online |
| Cost impact | Lower, and priced into most lab-grown stones already | Higher, and usually added on top of the stone price |
Does a certificate change what a diamond is worth?
No. A report describes a stone, it does not improve it. What a certificate buys you is verification: proof that an independent third party measured the stone, that the grades on the invoice are not the seller's own marketing, and that the number laser-inscribed on the girdle matches the report you can pull up online. That is worth real money on a stone that is worth real money.
It follows that certification is worth exactly as much as the doubt it removes. On a 1.5ct centre stone, one clarity grade can swing the price by thousands of dollars, so an independent report is essential. On a 0.05ct accent stone, no grade on earth moves the price meaningfully.
Essential Diamond Solitaire Studs
Starts at 0.5ct per stone, so every diamond in these is individually IGI-certified and laser-inscribed with its report number.
From HK$2,300 (single) or HK$4,300 (pair)
View productWhen is a certificate not worth paying for?
Here is the part most jewellers will not say out loud. Independent grading has a floor price. Below a certain stone size, that fee costs more than the diamond it is grading. Paying it does not protect you, it just moves money from your pocket to a laboratory for a piece of paper describing a stone worth less than the paper.
Carat Club Co. draws the line at 0.5ct. Stones of 0.5ct and above are individually IGI-certified, with the report number laser-inscribed on the girdle. Stones below 0.5ct are not certified by default. The threshold applies per stone, not per piece, so in a design with a 1.0ct centre and 0.1ct accents, the centre carries a certificate and the accents do not. If you want a sub-0.5ct stone certified anyway, we will arrange it on request.
Vanguard Men's Diamond Solitaire Studs
A 0.5ct entry point in S925 sterling silver, platinum-plated, with the diamond individually IGI-certified.
From HK$1,599 (single)
View productWhy tennis bracelets are the clearest example
A tennis bracelet is the test case for this whole argument. A 17cm line holds roughly 34 stones. Certifying every one of them individually costs HK$350 per stone with IGI, which adds around HK$11,900 to a bracelet whose diamonds are 0.05ct each. You would be paying close to the price of the bracelet again for a stack of paper.
So the certificate is not included in the base price of our tennis bracelets. If you want it, IGI certification is available on request at HK$350 per stone, and we will quote the exact number for your length. Most buyers decline once they see the arithmetic, and we think that is the correct decision. If you are weighing up length, stone size and metal, our tennis bracelet buying guide (written in Chinese) walks through the trade-offs in detail.
Seamless Diamond Tennis Bracelet
Certificate not included in the base price. IGI certification is available on request at HK$350 per stone.
From HK$13,999
View productHow do you check a certificate is genuine?
Three steps, and they take about a minute. Find the report number on the paperwork. Look for the same number laser-inscribed on the girdle of the stone, which you can see under 10x magnification and any jeweller can show you. Then type that number into the laboratory's own online verification tool and confirm the grades match. A seller who cannot show you the inscription, or whose report number returns nothing online, has told you everything you need to know.
Buying online adds one more question: who stands behind the piece afterwards. Carat Club Co. makes every piece to order in 2 to 3 weeks, covers it with a one-year free repair and a 7-day defect exchange, and does not accept returns. We ship to Hong Kong and 14 other APAC markets. For a fuller walkthrough of buying a real diamond online in Hong Kong, our guide to buying real diamonds online (written in Chinese) covers what to check before you pay.
Statement Diamond Solitaire Studs
At 3.0ct per stone this is where a certificate earns its keep, and each diamond is individually IGI-certified.
From HK$18,800 (single)
View productFrequently asked questions
Is a GIA certificate better than an IGI certificate?
Not for a lab-grown diamond. Both labs are independent, both inscribe the report number on the stone, and both publish verification online. GIA reports on lab-grown stones are rarer and typically cost more, which narrows your selection without telling you anything materially different about the diamond.
Are all of Carat Club Co.'s diamonds IGI-certified?
No, and we will not pretend otherwise. Diamonds of 0.5ct and above are individually IGI-certified. Stones below 0.5ct are not certified by default, because the grading fee would exceed the value of the stone. Certification for smaller stones is available on request.
Can I get a certificate for a stone under 0.5ct?
Yes. Ask us before you order and we will arrange IGI certification and quote the fee. For tennis bracelets the rate is HK$350 per stone, so a 17cm line of about 34 stones works out to roughly HK$11,900 on top of the bracelet price.
Does a certificate prove a diamond is real?
It proves what the stone is. An IGI report for a lab-grown diamond states that the stone is a laboratory-grown diamond and gives its 4Cs. Lab-grown diamonds are real diamonds: same carbon, same crystal structure, same hardness. The report confirms origin and quality, not authenticity in the sense of "is this glass".
