This article ("The value (quality) of a diamond is determined by the '4Cs'"), carat is 1 carat (ct) = 0.2g.WeightIt is not an index of size, so even if the carat weight is the same, the apparent size may vary slightly. This unit is also used for gemstones in general, such as rubies and sapphires, in addition to diamonds. Different gemstones have different specific gravities, so even if they are the same 1 carat, a 1 carat diamond and a 1 carat ruby ​​will have different apparent sizes. Also, even if they are the same shape and the same carat weight, each ruby ​​has a different depth, so the apparent size will be different. For this reason, when it comes to colored gemstones, they are often compared by their actual dimensions.

In the case of diamonds, if the cut standard is excellent, the size will not differ that much. Please refer to the table below for the approximate size of round brilliant cut diamonds.
A difference of 0.1ct will only change the diameter by about 0.4 to 0.7mm, but the difference is immediately noticeable when comparing. If it is about 0.05ct, you will not be able to tell the difference unless you look closely.If you want something a little larger, choose a stone that is about 0.1ct larger. If you want something a little smaller, choose a stone that is about 0.1ct smaller..

The preferred carat size has changed with the culture of the country and the times. Of course, it depends on the individual, but Japanese women tend to choose small, high-quality diamonds of around 0.3 carats. However, during the bubble era, diamonds of around 1 carat were preferred, even if it meant lower quality. If the economy improves in the future, the carat size may also increase.
But what about overseas? This is based on past experience, but people generally place more importance on carat and tend to choose larger diamonds. Overseas customers who come to our store are generally looking for diamonds over 1 carat. Japanese customers living overseas also tend to choose larger diamonds. This is a sign that Japan has a unique culture.

Do you know the origin of the word carat? The word carat comes from the seeds of carob. Carob seeds are very uniform in weight, about 0.2g. In the past, jewelers used carob as a counterweight on their scales to measure the weight of jewels. Later, in 1913, the United States adopted the metric carat system (unit: ct), and carat became the international standard.
Also, there are many appraisal agencies in the world, and each one displays the carat weight differently.
GIA, the international value standard, displays the value to two decimal places, such as 1.00ct, but Japan's largest Central Gem Laboratory (CGL) displays the value to three decimal places, such as 1.000ct.
At Houjudo, we handle both types of diamonds, but we have more GIA certified diamonds in stock.
If you would like to know more about GIA, please refer to the following pages.

▼What is a GIA certified diamond?

For engagement rings, the most commonly chosen carat weight is around 0.3ct. Many Japanese customers tend to value smaller rings and quality. However, at Hojudo, the price is reasonable, so many customers choose around 0.4ct.
0.5ct is generally considered large, while 1ct has a strong presence and you can see its size even from a distance.
If you aspire to a 1ct diamond and are particular about size, then you should think of 1ct or more; if you like flashy, larger accessories, then 0.5ct or more is the best choice; and if you don't want it to stand out too much, then 0.3ct is the best choice.

Some young customers in their teens and twenties who want to wear it casually as an accessory for everyday use choose 0.1-0.2ct diamonds, but as they get older, they tend to choose larger carats. Customers over 40 often prefer 0.5ct or more. So, if you are purchasing a diamond to last a lifetime, try to choose a slightly larger diamond. At Hojudo, the number of customers who choose 0.2ct is quite low compared to other brands.

The appropriate carat number will also vary depending on your height and finger size.
It's best to try it on and decide, but if you are tall, have long fingers, or have large fingers, choose a larger carat number. Conversely, if you are petite and have small fingers, you may want to choose a slightly smaller number.

When you try on a diamond ring for the first time, the diamond may seem large, but strangely enough, you soon get used to it. Therefore, if you decide on a smaller diamond right away, you will regret it, so try on several rings and take your time to choose.
(Some customers see a 0.2ct stone at another store, then see a 0.4ct stone at Houjudo and are hesitant because they think it is too big, but after trying on a few, they often order the 0.4ct stone and are very satisfied.)

It also depends on the design.A halo design, which has small diamonds surrounding the center diamond, creates volume. This makes even a relatively small diamond look larger. The balance with the ring design, such as the thickness of the arms, is also important.

Since rings are often viewed up close, many customers choose smaller diamonds that emphasize quality, but when it comes to pendant necklaces, many choose larger diamonds over quality.Generally speaking, 0.3ct is recommended for everyday wear, and 0.5ct or more is recommended for a lifetime ring. As with rings, many people choose larger carats as they get older.Also, some people who cannot normally wear rings choose pendant necklaces instead of engagement rings. Many people are particular about both size and quality when it comes to engagement necklaces, and many of our customers choose 0.3 to 0.4 carats.
As with rings, the key points to choosing a ring will depend on your preferences and body type. If you are tall or have a fuller figure, it is best to choose a larger carat number, and if you are petite, a smaller carat number is best.


If the design is a halo design, it will have volume, so even if you choose a relatively small diamond, it will appear large, so try to choose one that has a balance in mind.

Also, if you feel that the diamond in the prong ring inherited from your mother or grandmother is a little too big, we recommend remodeling it into a pendant. It's less expensive, and pendants are easier to wear, so you can wear them in more situations. Hojudo is also good at remodeling. Please refer to the detailed explanation on the page below.

▼For those renovating for the first time

Like necklaces, there are few opportunities to see earrings up close, so many customers place more importance on carat weight than quality.However, people tend to choose smaller diamonds than necklaces.If you have a 0.5ct pendant and 0.5ct earrings, the appearance will be very different, and the 0.5ct earrings will look very large.
Some people choose smaller rings of around 0.1ct for everyday use, but at Hojudo, most people choose diamonds in the 0.2ct or 0.3ct range.
If you plan to use it for a long time, it is best to choose one that is 0.3ct or more.
This also depends on your preferences, body type, and the size of your earlobes, but if you usually wear large earrings or have large earlobes, you should choose a slightly larger diamond. If you have small earlobes and want a more subtle look, you should choose a slightly smaller one.



In the case of earrings, a 0.1ct difference will have a much bigger impact on the look than a ring or pendant. We recommend trying them on first to see which size works best for you.
If you would like to know more or compare diamonds in person, please feel free to contact us or visit our store.