Emerald outline,brilliant fire.Carat to millimetres.
A trimmed-corner rectangle with brilliant faceting, the radiant is measured length × width in millimetres. This chart uses our own diamond measurements.
Why carat isn't the same as size.
Carat measures weight, not dimensions. The size you actually see is the stone's measurement in millimetres — and two diamonds of the same carat can look different sizes depending on how they are cut.
A shallow, well-spread stone shows more face-up area; a deep-cut one hides weight underneath. So when comparing diamonds, compare the millimetre dimensions, not just the carat weight.
"The number that decides how big a diamond looks isn't the carat — it's the measurement in millimetres."
The chart below gives you both, so you can picture the real size before you choose.
What makes the radiant special.
Radiant cuts pair the sleek trimmed-corner outline of an emerald with brilliant-cut faceting — so they sparkle like a round.
Unlike the emerald, the brilliant faceting masks inclusions, so eye-clean VS stones are easy to find.
Radiants range from near-square to distinctly elongated — the ratio decides the whole character.
Trimmed corners have no sharp points, making the radiant a robust choice for everyday wear.
What each size actually looks like.
These radiant shapes are drawn to relative scale from real face-up dimensions. Notice how gently size grows — a 2 carat is larger than a 1 carat, but not twice the size.
Drawn to relative scale for a well-cut radiant. On-screen sizes are proportional, not literal millimetres — see the chart below for exact dimensions.
Radiant Cut carat to millimetre chart.
Approximate face-up dimensions for a well-cut radiant. Sizes marked "Measured" reflect our own diamond measurements; larger sizes are extrapolated to the same proportions. Individual stones vary with cut and depth.
| Carat Weight | Size (mm) | L/W Ratio | Source |
|---|---|---|---|
| 0.25 ct | 4.2 × 3.0 mm | 1.40 | Measured |
| 0.50 ct | 5.3 × 3.8 mm | 1.40 | Measured |
| 0.75 ct | 6.1 × 4.4 mm | 1.40 | Measured |
| 1.00 ct | 6.7 × 4.8 mm | 1.40 | Measured |
| 1.25 ct | 7.2 × 5.2 mm | 1.40 | Approx. |
| 1.50 ct | 7.7 × 5.5 mm | 1.40 | Approx. |
| 1.75 ct | 8.1 × 5.8 mm | 1.40 | Approx. |
| 2.00 ct | 8.4 × 6.0 mm | 1.40 | Approx. |
| 2.50 ct | 9.1 × 6.5 mm | 1.40 | Approx. |
| 3.00 ct | 9.7 × 6.9 mm | 1.40 | Approx. |
| 4.00 ct | 10.6 × 7.6 mm | 1.40 | Approx. |
| 5.00 ct | 11.5 × 8.2 mm | 1.40 | Approx. |
Choosing the right proportions.
Two radiants of the same carat can look different depending on their length-to-width ratio. It comes down to taste — here are the main looks.
A near-square radiant — bold and modern, with brilliant fire.
A balanced rectangle — the most popular radiant proportion.
A longer rectangle that lengthens the finger and reads larger.
Four things worth knowing first.
Beyond size, a few radiant-specific pointers help you choose a stone that looks its best.
Square (~1.00) and rectangular (1.20–1.50) radiants look very different — decide the outline before anything else.
Brilliant faceting hides inclusions, so an eye-clean VS1–VS2 looks flawless at good value.
Radiants can gather a little warmth; near-colourless grades keep bigger stones bright in white metal.
With no points to chip, the radiant needs no special protection beyond a secure setting.
How the setting changes the size you see.
The same stone can look bigger or smaller depending on how it is set. If maximising visual size matters, the setting is as important as the carat weight.
A solitaire shows the true size; a halo frames it to read larger; a three-stone setting stretches the look along the finger. Choosing well means you can often get the presence you want without moving up in carat.
Browse radiant diamonds by size.
Found your size? Go straight to the collection — every stone IGI certified and lab grown.
Radiant size questions, answered.
The questions we hear most about radiant diamond sizing. If yours isn't here, just ask.
Chat on WhatsAppCompare sizes across every shape.
Still choosing a shape? Compare all cuts side by side →
Everything you need to choose with confidence.
Find your perfect radiant.
Every radiant is IGI certified and made to order, in the exact carat, ratio, and setting you choose. Not sure which size suits the hand? Tell us and we'll guide you.