How many grains are in one carat?

One carat equals approximately 3.086 grains. Conversely, one grain equals about 0.3240 carats. Three grains (194.4 mg) is close to one carat (200 mg) but not exact.

Is the grain used in the gemstone industry?

No. Gemstones use carats and points (1 carat = 100 points) exclusively. The grain is used in ammunition, archery, and some pharmacy contexts. The two units serve completely separate industries.

Why does the grain exist in all three English weight systems?

The grain was the fundamental small weight shared by the troy, avoirdupois, and apothecary systems. While the ounce and pound differ between systems, the grain is identical in all three - making it a reliable cross-system reference point.

Grains to Carats (gr to ct) Converter

1 gr = 0.324 ct

1 Grain equals 0.324 Carats (1 gr = 0.324 ct). Convert Grains to Carats with formula, table, and examples.

One grain equals approximately 0.3240 carats. The grain (64.80 mg) is roughly one-third of a carat (200 mg), making three grains almost exactly one carat. This near-integer ratio is coincidental but handy for mental math. The grain is the universal unit across all three English weight systems and remains standard in ammunition, while the carat rules the gemstone trade.

How to Convert Grains to Carats

ct = gr × 0.32399455

Multiply the value in Grains by 0.32399455

Take your value in Grains
Multiply by 0.32399455
Read the result in Carats

Common Grains to Carats Conversions

Grains (gr)	Carats (ct)	Status
1 gr	0.323995 ct
5 gr	1.619973 ct
10 gr	3.239946 ct
15 gr	4.859918 ct
20 gr	6.479891 ct
50 gr	16.199728 ct
55 gr	17.8197 ct
62 gr	20.087662 ct
77 gr	24.94758 ct
100 gr	32.399455 ct
115 gr	37.259373 ct
124 gr	40.175324 ct
147 gr	47.627199 ct
168 gr	54.431084 ct
200 gr	64.79891 ct
230 gr	74.518747 ct
300 gr	97.198365 ct
437.5 gr	141.747616 ct
480 gr	155.517384 ct
500 gr	161.997275 ct
1,000 gr	323.99455 ct
5,000 gr	1,619.97275 ct
7,000 gr	2,267.96185 ct

Good to Know About Grains to Carats Conversion

The grain's universality across English weight systems made it the only reliable bridge between troy (precious metals), avoirdupois (common goods), and apothecary (medicines) weights. A grain of gold, a grain of pepper, and a grain of quinine all weighed exactly the same 64.80 milligrams. This consistency was essential in an era when the same merchant might handle all three categories of goods.

Grains to Carats: What You Need to Know

A 1-carat diamond weighs about 3.086 grains. The Hope Diamond at 45.52 carats weighs roughly 140 grains. Ammunition reloaders who also collect gems might appreciate this conversion: a 150-grain rifle bullet and a 48.6-carat sapphire weigh the same. The grain connects the shooting range to the jewelry store through pure mathematics.

What is a Grain? gr

A grain is a unit of mass equal to exactly 64.79891 milligrams. It is the same in the avoirdupois, troy, and apothecaries' systems, derived from the 1959 international agreement defining the pound as exactly 0.45359237 kilograms.

Imperial Troy Apothecaries ammunition weight bullet measurement historical pharmacy

Learn more about Grain →

What is a Carat? ct

A carat is a unit of mass equal to exactly 200 milligrams (0.2 grams), used for measuring gemstones and pearls. Adopted internationally in 1907 by the Fourth General Conference on Weights and Measures.

Metric diamond weight gemstone grading pearl measurement

Learn more about Carat →

Going the other way? Use our Carats to Grains converter.

Grains to Carats FAQ

One carat equals approximately 3.086 grains. Conversely, one grain equals about 0.3240 carats. Three grains (194.4 mg) is close to one carat (200 mg) but not exact.
No. Gemstones use carats and points (1 carat = 100 points) exclusively. The grain is used in ammunition, archery, and some pharmacy contexts. The two units serve completely separate industries.
The grain was the fundamental small weight shared by the troy, avoirdupois, and apothecary systems. While the ounce and pound differ between systems, the grain is identical in all three - making it a reliable cross-system reference point.

Non-Frequently Asked Questions About Grains to Carats

Questions nobody should ask - but someone did.

Less impressive. A 2-carat engagement diamond (impressive) becomes 6.17 grains (sounds like a few crumbs). A 10-carat celebrity ring becomes 30.9 grains (sounds like a pinch of salt). The carat was wisely chosen to make gemstone weights sound substantial. Marketing matters even in measurement.
Three grains is 194.4 mg versus a true carat of 200 mg - an error of 2.8%. For casual estimation this is fine, but for gemstone pricing where value increases steeply with weight, 2.8% can mean hundreds of dollars. The gem trade rightly insists on exact carat measurements to the hundredth of a carat.
A 150-grain bullet would be called a 48.6-carat bullet. Ammunition packaging would read '20 rounds, 48.6 ct bullets, 12.96 ct powder charge.' This would make bullets sound like luxury items, confuse every shooter in America, and spark a wave of uncomfortable jewelry-ammunition comparison advertising. Best to keep grains for guns and carats for gems.