One Carat Diamond Ring Buying Guide

A one carat diamond engagement ring holds a special allure for those seeking a timeless and exquisite gemstone to symbolise a proposal. This guide is designed to help you navigate the intricate journey of choosing one. From understanding the 4Cs – carat weight, cut, colour, and clarity – to exploring key questions and what to consider before you buy. We will provide you with the knowledge to make an informed decision and find the perfect one carat diamond ring that matches your preferences, budget, and is a perfect symbol for your engagement.

‘Carat’ is a measurement of a diamond’s weight and is equivalent to 0.2 grams. Generally speaking, the heavier the carat weight, the larger the diamond will appear.

Every diamond is graded for several characteristics that reflect the beauty, rarity and value of the stone. These characteristics are known as the 4Cs: cut, colour, clarity, and carat.

When considering the size of a one carat diamond, it’s important to realise that size in millimetres often differs depending on the cut. In the table below we’ve collected some data on widths for one carat diamonds across a range of diamond shapes. As you can see a round diamond is usually around 6.34mm but a cushion diamond is slightly narrower at 5.7mm. These are not uniform widths for all one carat diamonds but they are a helpful guideline for their size.

Historically, diamonds were measured in relation to the number of carob seeds that equated to the same weight; a one carat diamond and a typical carob seed each equate to 0.20 grams. The metric has since evolved to become the highly accurate measurement now known as ‘carat’ weight, which is measured and recorded by diamond grading laboratories like the GIA.

There are a number of variables, other than carat weight, that can determine a diamond’s value. A one carat natural diamond engagement ring with the optimum grades or beauty and value for money could cost between £6,200 and £9,000 - or around £1,800 for a lab diamond. If you were to compromise greatly on the cut, clarity and colour grade of a natural one carat diamond, you could find options as low as £4,000. This, however, would directly impact the beauty of the stone; finding the right balance between the quality of the 4Cs is crucial for finding a diamond with brilliance, sparkle and lustre.

When budgeting for your engagement ring, consider the costs of the various ring designs that interest you. The simple the design, the more budget you can dedicate to the centre diamond of your ring! If you can’t find anything quite to your taste, we have an easy process to create your own engagement ring.

Here are some typical prices for different ring design styles, before the cost of the centre diamond is added:

• Solitaire from £850
• Diamond Band from £1,450
• Trilogy from £1,375
• Halo from £1,650

'Carat' is a measurement of weight, rather than size, equating to 0.20 grams. Technically speaking, not all one carat diamonds will appear the same size. A well cut, round brilliant diamond could look a totally different size to a poorly cut diamond with the exact same carat weight. Learn about cut grades and how this can affect the size that your diamond appears.

Diamond shape can greatly affect how big it appears; elongated shapes, such as pear or oval diamonds can look larger than round diamonds of the same carat weight. So when it comes to questioning how big a one carat diamond is, there’s no one, straight answer.

Here’s a reminder of how big one carat diamonds of different shapes appear when viewed from above:

The visible difference between a 1ct diamond and a 0.90ct diamond is minimal - but the price difference can be significant. Many engagement ring buyers will prefer to dedicate their budget to a really good quality, beautiful diamond between 0.90ct to 0.99ct, rather than aiming to hit the 1ct but compromising on the quality of the stone.

Remember, the cut quality of the diamond has the largest impact on the stone's beauty, closely followed by the colour grade. A slightly smaller, but a brighter, whiter and sparklier diamond will likely give you more joy than a larger stone that's dim, dull or yellow in tone.

These two photos show the same diamond ring. We’ve manipulated one of the images to make the stone slightly larger. One image reflects the size of a 0.90ct diamond, and the other a 1ct diamond. How noticeable is the 0.10ct difference to you?

Keep the following grade ranges in mind:

• Triple Excellent cut or XXX - meaning Excellent cut, Excellent polish, and Excellent symmetry, or at the very least Very Good. Only round diamonds receive a cut grade, so look at polish and symmetry for other diamond shapes.
• D to F colour, or down to G or H if choosing a yellow gold ring
• VS2 to SI1 clarity, or slightly higher for step cut diamonds, like emerald cuts

These grade boundaries will find you the most aesthetically beautiful diamonds - bright and rich in brilliance, whilst ensuring value for your money. Don’t get caught out by qualities that sound great, but in reality will cost you more for negligible benefit: for example, a higher clarity grade than VS2 will cost more money but will not be noticeable to the naked eye.

Connect with a Queensmith gemmologist. Let them know your rough budget, and they’ll prepare a selection of the best diamonds or gemstones for your ring ahead of your appointment. No complex decisions, just great value for money.

The average carat size for engagement ring buyers is 1.25ct at Queensmith, as detailed in our annual ring trend report. The average carat size for UK engagement ring buyers is closer 1ct, and you'll notice this vary by location, with hubs like London seeing larger carat weights purchased. The rise in popularity of lab diamonds, which have a lower cost-per-carat than natural diamonds, means the average carat weight is increasing.

You shouldn’t put too much pressure on buying a one carat diamond; as there are lots of alternatives that will make for a beautiful engagement ring.

Gemstones like sapphires, rubies and emeralds retail at a significantly lower cost than diamonds.

Lab grown diamonds can cost typically 60%, or even up to 80% less than a natural, mined diamond. Unlike diamond simulants like moissanites, lab diamonds are 100% real diamonds, and are visually and physically identical to natural diamonds, so are a great way to ensure a large diamond at an exceptionally reasonable price.

If you’d like a little more information, know exactly what you want, or would like to hear from the experts, we’re here to help - just drop us a message.

At our Hatton Garden Jewellers, each of our consultants are trained gemmologists, with the expertise and passion to help you find the perfect diamond and engagement ring. Whether you’re looking for a one carat diamond, or want to know a little more about budgeting and what you can find for your money, our gemmologists are on hand to help. Contact us to learn more or book an appointment.