Size Guide

Round Gemstone Millimeter to Carat Conversion

Understanding gemstone sizes can be tricky since carat weight measures mass, not size. However, round gemstones follow a standard millimeter-to-carat conversion based on their diameter. Use the image and chart below to find the approximate size and weight for your round gemstones.

Approx. Carat Weight Approx. Diameter (mm)
0.25ct 4mm
0.50ct 5mm
0.75ct 5.8mm
1.00ct 6.5mm
1.25ct 7.0mm
1.50ct 7.4mm
1.75ct 7.8mm
2.00ct 8mm
2.25ct 8.5mm
2.50ct 8.8mm
2.75ct 9.0mm
3.00ct 9.4mm

Oval Gemstone Millimeter to Carat Conversion

Oval gemstones tend to appear larger than round stones of the same carat weight due to their elongated shape. Since ovals vary in length-to-width ratio, their size may differ slightly. The image and chart below provide an approximate millimeter-to-carat conversion to help you visualize gemstone proportions.

Approx. Carat Weight Approx. Diameter (mm)
0.25ct 5.0x3.5mm
0.50ct 6.0x4.0mm
0.75ct 7.0x5.0mm
1.00ct 8.0x5.5mm
1.25ct 8.5x6.0mm
1.50ct 9.0x6.5mm
1.75ct 9.5x7.0mm
2.00ct 10.0x7.5mm
2.25ct 10.5x7.8mm
2.50ct 11.0x8.0mm
2.75ct 11.5x8.5mm
3.00ct 12.0x9.0mm

Which Size is Right for Me?

Choosing the perfect gemstone size depends on your personal style, the type of jewelry, and how bold you want your piece to look. Below is a guide to help you decide:

For Rings

The gemstone size dramatically impacts the ring’s look. Here’s what to expect:

  • 0.25 - 0.75 ct – Delicate, minimal, perfect for stacking rings or subtle everyday wear.
  • 1.00 - 1.50 ct – Classic and elegant, an ideal size for engagement rings and everyday rings.
  • 2.00 - 3.00 ct – Statement-making, bold yet wearable for those who love a luxurious look.
  • 3.00+ ct – Ultra-luxurious, a true showstopper with serious sparkle.

For Earrings

Earrings should be noticeable yet balanced for your style.

  • 0.25 - 0.50 ct per ear – Subtle and understated, great for everyday wear.
  • 1.00 ct per ear – A perfect balance of elegance and sparkle.
  • 1.50 - 2.00 ct per ear – A bold and dazzling choice.
  • 2.50+ ct per ear – High-impact, red carpet-worthy sparkle.

For Necklaces & Pendants

Larger gemstones tend to stand out more in necklaces.

  • 0.50 - 1.00 ct – Dainty and delicate, ideal for everyday wear.
  • 1.50 - 2.00 ct – A noticeable yet refined sparkle.
  • 2.50 - 3.00 ct – Luxurious and eye-catching, a true centerpiece.
  • 3.00+ ct – Bold and glamorous, perfect for statement jewelry.

Other Things to Consider

Finger & Hand Size: Smaller hands may find 1.00 - 1.50 ct rings look substantial, while larger hands may prefer 2.00+ ct.
Setting Style: A halo setting can make a gemstone appear larger, while a bezel setting may contain the look more.
Everyday vs. Occasion: If it’s for daily wear, you might want a smaller, low-profile size, while statement pieces can be larger and bolder.

✨ Need Help Choosing?

If you're unsure which gemstone size is right for you, feel free to contact us—we’re happy to help!