0.4 Carat Round Diamond Prices
Updated
On Nov 7, 2026, a 0.4 carat round natural diamond averaged $770 across 133,381 listings.
| Natural | |
|---|---|
| Average price | $770 |
| Listings | 133,381 |
| Change in 1 month | -2.65% |
Source: StoneAlgo Diamond Price Index
0.4 carat round diamond prices usually range from $323 to $1,664. In the last month, prices for these diamonds are down 2.65%.
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StoneAlgo developed our Visual Carat metric to help you understand whether your diamond looks larger or smaller than its actual carat weight implies.
For example, a 1 carat diamond could have a Visual Carat of 1.05 (meaning it looks like your average 1.05 carat diamond) or a smaller Visual Carat like 0.95 (meaning it looks like a 0.95 carat diamond when viewed from above).
How sparkly will your diamond look in person? Our cut score uses each diamond’s unique dimensions to determine just how perfectly it’s cut (and how well it will reflect light).
Cut score is based on a 10-point scale and we typically recommend looking for round diamonds that score a 7.5 or better.
Length-to-width ratio is calculated by dividing the widest part of the diamond by the narrowest part. A length-to-width ratio of 1.00 would be a perfect circle or square. As the ratio rises above 1 the diamond will begin to look more oval or rectangular. For round diamonds you should shoot for a ratio as close to 1.00 as possible and for fancy shapes it really comes down to a matter of preference.
Need help setting your budget? Check out our diamond price calculator to explore diamond prices.
The weight of your diamond and the most common measure to describe diamond size. Our Visual Carat Weight measurement is an even more accurate measure of how large the diamond will actually look based on its surface area, described in terms of carat weight.
The GIA grades diamonds on a scale of D (colorless) through Z (light color). StoneAlgo only shows colorless (D - F), near colorless (G - J), and K color diamonds (faint colored). The most common color grade for diamond engagement rings is H color.
Clarity grades measure the type, size, and location of inclusions on the surface or within the diamond. The most common clarity grades for engagement rings are VS2 and SI1.
1 in 3 diamonds exhibits some degree of fluorescence when exposed to UV light. Some fluorescence can actually be a good thing if you’re shopping for a near colorless (G - J) or faint colored (K) diamond.
After diamonds are cut into their final form, they are polished to be as sparkly as possible. Most people choose very good polish or better.
Sometimes diamonds are cut in a way that is not symmetrical, and this can prevent the diamond from sparkling at its best. We recommend excellent symmetry.
The ratio is calculated by dividing the diamond’s length by its width. For round cut diamonds the ideal L/W ratio is 1.00 - 1.05 while for some fancy shapes it is more a matter of style and preference.
The diamond’s height as a percentage of it’s width.
The width of the table (the flat top of the diamond) as a percentage of the diamond’s full width.
How sparkly will your diamond look in person? Our cut score uses each diamond’s unique dimensions to determine just how perfectly it’s cut (and how well it will reflect light).
Cut score is based on a 10-point scale and we typically recommend looking for round diamonds that score an 7.5 or better.
This is the rating for diamond cut quality the grading agency provided for the diamond. While we believe you should always look at this value, we recommend relying on StoneAlgo's Cut Score as it provides much more granularity.
Like a Zillow Zestimate for your diamond. Our Fair Price Estimate is updated daily based on live diamond prices from top online jewelers. Please keep in mind that every diamond is unique and some real-life diamond prices will differ meaningfully from our fair price estimate.
This fair price estimate is not an offer to buy or sell this diamond.