Carat to Gram Converter

Carat to Gram Conversion Basics

The carat is the standard unit of weight for gemstones and pearls. One carat is defined as exactly 0.2 grams, or 200 milligrams. This standard was adopted internationally in 1907 so that diamond and gemstone weights would mean the same thing everywhere in the world.

In practice, the carat is subdivided into 100 points — so a 0.25 ct stone is often called a "25 pointer" in the trade. Jewellers weighing gold use grams, which is why converting between carats and grams comes up constantly when pricing jewellery.

Common Carat to Gram Conversions

Carats (ct)	Grams (g)	Milligrams (mg)
0.10 ct	0.02 g	20 mg
0.25 ct	0.05 g	50 mg
0.50 ct	0.10 g	100 mg
1 ct	0.20 g	200 mg
2 ct	0.40 g	400 mg
3 ct	0.60 g	600 mg
5 ct	1.00 g	1000 mg
10 ct	2.00 g	2000 mg

Carat vs. Karat — Don't Confuse Them

Carat (ct) measures gemstone weight. Karat (k / kt) measures gold purity — 24 karat is pure gold, 18 karat is 75% gold. They sound identical but mean completely different things.

Frequently Asked Questions

Is a carat a unit of weight or size?

Weight. Two 1 carat gems can look very different in size — a 1 ct diamond (~6.5 mm round) appears larger than a 1 ct sapphire because diamond is less dense.

How do I convert milligrams to carats?

Divide milligrams by 200. For example, 500 mg ÷ 200 = 2.5 carats.

What is a point in gemstone weight?

One point is one-hundredth of a carat (0.01 ct = 2 mg). Stones under 1 ct are commonly priced per point.