1 carat diamond rings
The most requested size, and the easiest to overpay for.
By the CTJ Jewellery team, led by founder Greg Ward · Updated September 2026 · Editorial policy
Key facts
- A 1.00ct round is about 6.4mm across
- Price per carat steps up at 1.00ct
- 0.90 to 0.99ct looks the same for less
- Cut matters more than colour or clarity
- Natural or lab-grown
- Settings from $2,200, diamond quoted separately
How big is a 1 carat diamond?
Carat is weight, not size. A well-cut 1.00ct round measures about 6.4mm across. Ovals, pears and marquise cuts spread wider for the same weight, so they look larger on the hand.
| Shape | Approximate face-up size at 1.00ct |
|---|---|
| Round | 6.4mm |
| Oval | 7.7 × 5.7mm |
| Cushion | 5.8 × 5.8mm |
| Princess | 5.5 × 5.5mm |
| Emerald | 7.0 × 5.0mm |
| Radiant | 6.5 × 5.2mm |
| Pear | 8.5 × 5.5mm |
| Marquise | 10.0 × 5.0mm |
Approximate. Every diamond’s proportions differ.
What affects the price of a 1 carat diamond?
Price per carat jumps at the 1.00ct mark because buyers want the round number. After weight, cut quality has the biggest effect on how the diamond looks, then colour and clarity.
Natural diamonds carry a much higher price than lab-grown diamonds of the same grades. See natural diamond prices and the diamond price guide.
Is a 0.90 carat diamond a better buy?
A diamond just under 1.00ct can cost noticeably less than one just over it. The difference in width is around 0.1 to 0.2mm, which no one can see on the hand. If the round number doesn’t matter to you, ask us to include 0.90 to 0.99ct stones in your shortlist.
Which grades should I choose for a 1 carat diamond?
- Cut: Excellent for rounds; judge fancy shapes by eye
- Colour: G to H looks white in most settings; I to J can suit yellow or rose gold
- Clarity: VS2 or an eye-clean SI1, checked on video
- Report: GIA for natural, IGI or GIA for lab-grown
More detail in the four Cs.
Natural or lab-grown at 1 carat?
Both are real diamonds with the same hardness and sparkle. A natural diamond is finite and formed over billions of years. A lab-grown diamond gives more size and higher grades for the budget. We show both side by side so you can decide by eye and by price. Natural and lab-grown compared.