This article ("The value (quality) of a diamond is determined by the '4Cs'."As mentioned elsewhere, 1 carat (ct) = 0.2gweightThis is a unit of measurement. It is not an indicator of size, so even with the same carat weight, the apparent size can vary slightly. Also, this unit is used not only for diamonds but also for gemstones in general, such as rubies and sapphires. Since the specific gravity changes depending on the gemstone, the apparent size of a 1ct diamond and a 1ct ruby ​​will differ even if they are both 1ct. Furthermore, even among rubies, the depth varies from one to another, so even if they are the same shape and carat weight, their apparent size will differ. For this reason, in the case of colored gemstones, it is often better to compare them by their actual dimensions.

When comparing diamonds, if the cut standard is excellent, the size difference won't be that significant. Please refer to the table below for approximate sizes of round brilliant cut diamonds.
A difference of 0.1ct only changes the diameter by about 0.4-0.7mm, but the difference is immediately noticeable when comparing them. A difference of around 0.05ct is so small that you can't tell the difference unless you look very closely.If you want something a little bigger, choose one that's about 0.1ct larger; if you want something a little smaller, choose one that's about 0.1ct smaller..

The preferred carat size has changed with the culture of a country and the trends of the times. Of course, it varies from person to person, but Japanese women tend to choose smaller, high-quality diamonds of around 0.3 carats. However, during the bubble economy era, larger diamonds of around 1 carat were preferred even if the quality was lower. If the economy improves in the future, carat sizes may also increase.
On the other hand, what about overseas? Based on our experience, people generally prioritize carat weight and tend to choose larger diamonds. Our overseas customers who visit our store are usually looking for diamonds of 1 carat or more. Japanese customers living abroad also tend to choose larger diamonds. This is a reflection of Japan's unique culture.

Do you know the origin of the word "carat"? The word "carat" comes from the seed of the "carob" plant. Carob seeds are very uniform in weight, weighing approximately 0.2g each. In the past, jewelers used these carob seeds as weights on their scales to weigh gemstones and other items. Later, in 1913, the United States adopted the metric carat system (unit: ct), and the carat became the international standard.
Furthermore, while there are many appraisal institutions around the world, the way carat weights are displayed varies depending on the institution.
The GIA, which sets the international standard for value, displays carat weights to two decimal places, such as 1.00ct, while Japan's largest gemological laboratory, the Central Gem Laboratory (CGL), displays weights to three decimal places, such as 1.000ct.
At Hojudo, we handle both types of diamonds, but we stock more diamonds certified by the GIA.
If you'd like to learn more about GIA, please refer to the following page.

▼What is a GIA-certified diamond?

For engagement rings, the most commonly chosen carat size is around 0.3ct. Many Japanese customers prefer smaller rings and prioritize quality. However, at Hojudo, due to our reasonable prices, many customers choose rings around 0.4ct.
A 0.5ct diamond is generally considered large, and a 1ct diamond has a noticeable presence and its size is apparent even from a distance.
If you aspire to own a 1-carat diamond and prioritize size, you should aim for 1 carat or larger. If you prefer flashy, larger jewelry, aim for 0.5 carats or larger. If you want something less conspicuous, aim for 0.3 carats.

While some young customers in their teens and twenties who want a diamond to wear casually as an accessory for everyday use choose 0.1 to 0.2 carats, there is a tendency for people to choose larger carats as they get older. Customers in their forties and older often prefer 0.5 carats or more. Therefore, if you are purchasing a diamond that will last a lifetime, you should choose a slightly larger diamond. At Hojudo, the number of customers who choose 0.2 carats is considerably smaller compared to other brands.

In addition, the ideal carat size for you will vary depending on factors such as your height and finger size.
It's best to try them on before deciding, but if you're tall, have long fingers, or have larger fingers, choose a larger carat size. Conversely, if you're petite and have small fingers, you might want to choose a slightly smaller size.

When you try on a diamond ring for the first time, the diamond might seem large, but strangely enough, you quickly get used to it. Therefore, if you hastily decide on a smaller diamond, you might regret it, so try on several rings and choose carefully.
(Some customers who have seen 0.2ct diamonds at other stores are hesitant to buy 0.4ct diamonds at Hojudo, thinking they are "too big." However, in many cases, after trying on several diamonds, they end up ordering a 0.4ct diamond and are very satisfied.)

It also depends on the design. If it's a design like a halo design, where small diamonds surround the center diamond, it will have more volume.Therefore, even relatively small diamonds can appear larger. The balance with the ring design, such as the thickness of the band, is also important.

Since rings are often viewed up close, many customers choose smaller diamonds that prioritize quality. However, with pendant necklaces, customers tend to choose larger diamonds rather than focusing on quality.Generally speaking, 0.3ct is suitable for everyday wear, but if you want a ring that you can wear for a lifetime, 0.5ct or more is recommended. Similar to rings, many people choose larger carat sizes as they get older.Also, some people who don't usually wear rings choose a pendant necklace instead of an engagement ring. When it comes to engagement necklaces, many people are particular about both the size and quality, and at our store, many customers choose a carat size of 0.3 to 0.4 carats.
Just like with rings, the points to consider when choosing a diamond will vary depending on your preferences and body type. If you are tall or have a fuller figure, it's best to choose a larger carat size, while if you are petite, a smaller carat size would be a good choice.


If you choose a halo design, it will have more volume, so even if you choose a relatively small diamond, it will appear larger. Try to choose one that balances well with your existing diamonds.

Also, if you feel that the diamond in a solitaire ring inherited from your mother or grandmother is "a little too big," we recommend having it remodeled into a pendant. It's more affordable, and a pendant is easier to wear casually, so it will have more occasions to be worn. Hojudo specializes in jewelry remodeling. Please refer to the page below for more details.

▼For those undertaking renovations for the first time

Just like necklaces, earrings are rarely viewed up close, so many customers prioritize carat weight over quality.However, people tend to choose smaller diamonds rather than necklaces.The appearance is quite different between a 0.5ct pendant and a 0.5ct earring; the 0.5ct earring looks very large.
While some people choose smaller diamonds of around 0.1ct for everyday wear, at Hojudo, most customers choose diamonds in the 0.2ct or 0.3ct range.
Considering that it will be worn for a long time, something of 0.3 carats or more would be best.
This also depends on your preference, body type, and earlobe size, but if you usually wear large earrings or have larger earlobes, choose a slightly larger diamond. If you have small earlobes and want something less noticeable, choose a slightly smaller one.



With earrings, a difference of 0.1ct can significantly alter the overall look compared to rings or pendants. We recommend trying them on before making your selection.
If you'd like to learn more or compare diamonds in person, please feel free to contact us or visit our store.