Yes. We recommend comparing a diamond's measurements as well as its carat weight, especially when you are deciding between several loose lab diamonds with similar prices or specifications.
Carat tells us how much a diamond weighs. It does not tell us exactly how large the diamond will look from above. Two diamonds with the same carat weight can have noticeably different measurements, proportions and face-up appearances.
When comparing diamonds, we therefore look beyond carat alone. By considering measurements alongside shape, cut quality, colour, clarity and certification, we can make a more informed decision and identify the specification that offers the best visual value.
(Related: How Do I Know If a Diamond Price Is Fair?)
Why Carat Weight Alone Does Not Tell the Whole Story
Carat is a measurement of weight, not visible size.
One carat equals 200 milligrams, but the way that weight is distributed throughout a diamond can vary. A diamond may be deeper, wider, or proportioned differently from another diamond with the same carat weight.
For example, imagine two round diamonds that both weigh 1.00 carat. One may measure approximately 6.30 mm across, while another may measure closer to 6.45 mm. Both weigh the same, but the second diamond can appear slightly larger when viewed from above.
This is why simply searching for "1 carat" does not necessarily identify the diamond that will provide the largest or most attractive face-up appearance.
When we compare loose lab diamonds, measurements give us another important piece of information that carat weight cannot provide by itself.
What Diamond Measurements Tell You
A diamond's measurements are normally shown in millimetres.
For a round diamond, you may see a measurement such as:
6.40 x 6.43 x 3.95 mm
The first two figures represent the diamond's length and width, while the third represents its depth.
For fancy shapes, measurements are often presented in the same format, such as:
8.20 x 5.60 x 3.50 mm
This can be particularly useful because elongated shapes can have very different length-to-width ratios despite having similar carat weights.
When comparing diamonds, we can use these measurements to understand:
- How large the diamond appears from above
- Whether the stone is relatively deep or shallow
- The diamond's length-to-width ratio
- How two diamonds of similar carat weight compare visually
- Whether one diamond may be carrying more weight in its depth
Measurements should not replace other diamond specifications, but they are an important part of the comparison.
Carat Weight vs Measurements: What Should You Prioritise?
We do not recommend choosing between carat and measurements as though one is always more important.
Instead, use them for different purposes.
Carat weight tells you the diamond's actual weight and is an important part of its specification and pricing.
Measurements help you understand its physical dimensions and potential face-up size.
If two diamonds have similar colour, clarity, cut quality and certification, measurements can help us decide which one provides the more appealing combination of size and price.
This is particularly relevant when buying a diamond online because you may not have the opportunity to compare the stones physically before purchasing.
Why Two Diamonds With the Same Carat Can Look Different
The difference usually comes down to how the diamond's weight is distributed.
Consider two 2.00 carat round diamonds. If one has a greater proportion of its weight below the girdle, it may have a smaller diameter than another diamond that distributes more of its weight across its width.
The deeper diamond is not automatically a poor diamond. Depth is part of the overall cut structure, and measurements must always be considered alongside proportions and cut quality.
The key point is that 2.00 carats does not automatically mean the same visible size for every diamond.
This is why measurements are particularly useful when comparing multiple stones.
Measurements Matter Even More With Fancy Diamond Shapes
Measurements can be especially important when buying oval, pear, emerald, radiant, cushion or marquise diamonds.
A 2.00 carat oval diamond, for example, could have a relatively elongated appearance, while another 2.00 carat oval could look wider and shorter.
Neither shape is inherently better. It comes down to personal preference and the look you want.
The length-to-width ratio can help you understand this difference.
Example: Comparing Oval Diamonds
Suppose we are comparing two 2.00 carat oval diamonds:
Diamond A: 10.50 x 7.00 mm
Diamond B: 9.80 x 7.40 mm
Diamond A has a more elongated outline. Diamond B is shorter and wider.
Although they have the same carat weight, they can create quite different appearances once set into a ring.
This demonstrates why carat weight alone is not enough when choosing a fancy shape.
How to Compare Measurements Properly
When comparing measurements, we recommend looking at the complete specification rather than focusing on one number.
1. Compare length and width
Start with the first two measurements.
These provide the clearest indication of the diamond's face-up dimensions.
For round diamonds, the two numbers should usually be very close. A measurement such as 6.40 x 6.43 mm indicates a nearly circular outline.
For fancy shapes, the relationship between length and width becomes much more noticeable.
2. Look at the depth measurement
The third measurement shows the diamond's depth.
A deeper diamond may carry more of its weight vertically rather than across its visible surface.
However, we should not automatically reject a diamond simply because its depth appears higher. Diamond proportions work together, and the effect depends on the shape and cut.
3. Consider the length-to-width ratio
For elongated shapes, divide the length by the width to understand the approximate ratio.
For example:
8.00 mm ÷ 5.00 mm = 1.60
That gives the diamond an approximate 1.60 length-to-width ratio.
This can be useful when comparing several oval, pear or other elongated diamonds.
4. Compare measurements with price
This is where measurements become particularly useful for value comparisons.
If two diamonds have similar colour, clarity, cut characteristics and certification, but one has slightly larger face-up measurements at a similar price, it may deserve closer consideration.
However, we should never choose solely on the basis of the largest measurements.
A diamond that looks larger but has undesirable proportions or poor light performance may not represent better value.
Should You Choose the Diamond With the Largest Measurements?
Not necessarily.
The objective is not simply to find the diamond with the largest possible dimensions.
We want a balanced diamond that offers strong visual appearance, appropriate proportions, attractive cut quality and a sensible price.
For example, a diamond may have a large face-up appearance because it is cut relatively shallow. While this can make the stone look larger, it can also affect how effectively the diamond handles light.
This is why measurements should be treated as one part of the decision-making process.
A better approach is to ask:
Does this diamond provide the appearance and quality I want for the price I am paying?
That is a much more useful question than simply asking which stone has the highest carat weight.
(Related: Should I Compare Diamond Certificates Before Buying?)
How Measurements Can Help When Comparing Certified Lab Diamonds
When buying certified lab diamonds, we recommend comparing the certification details and measurements together.
A certificate can provide important information about the diamond's carat weight, measurements, proportions, colour, clarity and other characteristics.
Instead of comparing two stones by carat alone, create a simple side-by-side comparison.
For example:
| Specification | Diamond A | Diamond B |
|---|---|---|
| Carat | 1.00 ct | 1.00 ct |
| Measurements | 6.30 x 6.33 mm | 6.43 x 6.46 mm |
| Colour | E | F |
| Clarity | VS1 | VS1 |
| Certification | Certified | Certified |
| Price | £1,000 | £1,050 |
Diamond B costs more, but the additional cost may be justified if its overall specification and visual appearance are preferable.
On the other hand, Diamond A may represent better value if the visual difference is negligible to you.
There is no single specification that automatically wins. The right choice depends on what you value most.
Do Measurements Matter More Than Carat for Maximum Visual Size?
If your priority is the largest possible face-up appearance, measurements deserve significant attention.
A diamond with a slightly lower carat weight can sometimes have similar or even larger visible dimensions than a heavier diamond, depending on its proportions and shape.
For example, when comparing a 0.95 carat stone with a 1.00 carat stone, we should not assume that the 1.00 carat diamond will automatically look larger.
This is one reason we encourage buyers to compare actual measurements when choosing between closely matched diamonds.
However, visible size is only one consideration. Cut quality, brilliance and overall appearance remain important.
Measurements Should Be Used With Cut Quality
For round diamonds in particular, cut quality deserves careful attention.
Measurements alone cannot tell us whether a diamond will have excellent brilliance, fire and scintillation.
A stone may have attractive dimensions but still be less visually impressive than another diamond with slightly smaller measurements and stronger light performance.
When comparing diamonds, we therefore recommend reviewing:
- Carat weight
- Measurements
- Cut quality
- Depth and table
- Colour
- Clarity
- Certification
- Shape
- Price
- Available images or videos
Looking at the full specification prevents us from making a decision based on a single number.
A Practical Way to Compare Diamonds Before Buying
If you are comparing several loose lab diamonds, use the following process.
Step 1: Choose your preferred shape.
Decide whether you want a round, oval, emerald, cushion, radiant, pear or another shape.
Step 2: Set your approximate carat range.
Carat remains useful for narrowing your search and understanding the general size category.
Step 3: Compare measurements.
Look at the length and width rather than carat alone.
Step 4: Check the proportions.
Review depth, table and other available specifications.
Step 5: Verify the certification.
Make sure the diamond's certificate corresponds with the stone you are considering.
Step 6: Compare colour and clarity.
Avoid paying for specifications that are unlikely to provide a meaningful visual improvement.
Step 7: Compare prices.
Once the diamonds are reasonably comparable, examine the price differences.
Step 8: Review the actual diamond.
Where images, videos or other visual information are available, use them to assess the stone rather than relying entirely on numerical specifications.
This approach helps us choose based on overall value rather than one headline specification.
When Carat Weight Should Still Be Your Main Reference
Although measurements are important, there are situations where carat remains the most useful starting point.
If you have a specific target size, such as a 1.00 carat engagement diamond, carat can help you establish the category you want.
It is also useful when comparing prices across similar specifications.
The mistake is not using carat. The mistake is assuming that carat tells us everything about visible size.
We should think of carat as the starting point and measurements as an additional layer of information.
How to Find the Best Value Without Overspending
The best value diamond is rarely the one with the highest specification across every category.
For most buyers, a more sensible strategy is to identify the specifications that create a strong visual result and avoid paying substantial premiums for characteristics that make little visible difference.
For example, moving from one clarity grade to another may have little practical impact if both diamonds appear eye-clean. Similarly, a small difference in colour may be less important than the overall cut and appearance.
Measurements can then help us compare the physical size of diamonds that meet our other requirements.
This creates a more balanced approach to diamond buying.
Should You Compare Measurements Instead of Carat Only?
Yes, we recommend comparing measurements instead of relying on carat alone.
Carat tells you the diamond's weight, while measurements help you understand its physical dimensions and potential face-up appearance. The difference can be especially important when comparing diamonds of the same carat weight or when choosing elongated fancy shapes.
However, measurements should never be considered in isolation.
The strongest buying decision comes from comparing measurements alongside cut quality, proportions, colour, clarity, certification and price. By looking at the complete specification, we can identify diamonds that offer the appearance and quality we want without unnecessarily increasing the budget.
When comparing loose lab diamonds, a few millimetres can make a meaningful difference in how a stone looks. Taking the time to compare those measurements can therefore help us make a more informed choice and find better overall value.