Carat and karat sound alike but refer to two different measurements. A carat (ct) is a unit of weight used to measure gemstones such as diamonds; one carat equals 200 milligrams (0.2 grams).
A karat (K) measures the purity of gold, with 24 karat representing pure gold. Understanding the difference helps you assess both the value of a gemstone and the quality of the metal in your jewellery.
Carat explained
- Weight, not size: Carat refers to weight, not physical dimensions. Two diamonds of the same carat may look different in size depending on their cut and shape.
- Pricing: Larger carat weights are rarer and therefore command higher prices. However, cut, colour and clarity also influence value.
- Fractions and multiples: Diamonds and gemstones can be described using fractional carats (e.g., 0.25 ct) or total carat weight when multiple stones are combined.
Karat explained
- Purity scale: Karat denotes how many parts out of 24 are pure gold. For example, 18 K gold is 18 parts gold and 6 parts alloy (75 % pure), while 9 ct gold is 9 parts gold and 15 parts alloy (37.5 % pure).
- Durability: Higher‑karat gold contains more pure gold and is softer. Lower‑karat alloys such as 14 K or 9 ct are harder and more suitable for everyday wear.
- Colour and cost: A higher gold content produces a richer yellow colour but also increases the price.
Why understanding both matters
Knowing both the carat weight of gemstones and the karat purity of metals helps you evaluate value and durability. A 1 ct diamond set in 18 K gold will be pricier than a 0.5 ct stone in 9 ct gold because it combines a heavier gem with higher gold purity.
FAQs
- What is a good carat weight for an engagement ring? The average UK engagement ring is around 0.60 ct, but the right weight depends on your budget and preferences.
- Is higher‑karat gold always better? Not necessarily. Higher‑karat gold looks richer but is softer. Many people choose 14 K or 18 K to balance colour and durability.
- Can a 1 ct diamond look larger than another? Yes. A diamond with an excellent cut or an elongated shape (such as oval or marquise) can appear larger than a poorly cut 1 ct round stone.
Last updated: March 2026