Convert Carat to Grain (ct → gr)
The carat equals 200 milligrams exactly and is the universal unit for gemstone and diamond weight in jewelry.
Carat to Grain Conversion Table
10 common values| Carat | Grain |
|---|---|
| 1 ct | 3.086472 gr |
| 5 ct | 15.432358 gr |
| 10 ct | 30.864717 gr |
| 25 ct | 77.161792 gr |
| 50 ct | 154.32358 gr |
| 100 ct | 308.64717 gr |
| 250 ct | 771.61792 gr |
| 500 ct | 1,543.2358 gr |
| 1,000 ct | 3,086.4717 gr |
| 5,000 ct | 15,432.358 gr |
How to Convert Carat to Grain Manually
Step by StepConverting carats to grains is straightforward: multiply by the conversion factor. Follow these three steps to do it by hand or in your head.
- 1Take your value in caratsStart with the number of carats (ct) you want to convert.
- 2Multiply by 3.086472The conversion factor from ct to gr is 3.086472. Multiply your value by this number.
- 3Read the result in grainsThe result is your value in grains (gr).
Formula
Multiply the value in carats by 3.086472. For the reverse direction, multiply by 0.323995.
gr = ct × 3.086472ct = gr × 0.323995Tips
Use these in everyday conversions- 1 carat = 200 mg = 0.2 g exactly since 1907.
- Carat (gem weight) and karat (gold purity, 24 K = pure) are different words with different meanings.
- A carat is divided into 100 points; a 0.25 ct diamond is called a "25-pointer".
Common Mistakes
Avoid these- Confusing carat (mass) with karat (gold purity).
- Assuming a 2-carat diamond is twice the physical size of a 1-carat — volume scales with cube root of mass.
- Using "karat" on gemstone certificates — international standard is "carat" spelled with a C.
About Carat and Grain
What is the Carat?
The carat equals exactly 200 milligrams (0.2 g) and is the universal unit for gemstone and diamond weight in the global jewelry industry. The word derives from the Greek 'keration' and the Arabic 'qīrāṭ,' both referring to carob seeds, which were once used as natural counterweights for weighing gems because they have remarkably uniform mass. The metric carat was standardized in 1907 at exactly 200 mg, replacing dozens of regional carat values that had varied between 188 and 213 mg. A 1-carat diamond is roughly 6.5 mm in diameter, and the famous Hope Diamond weighs 45.52 carats. The carat is distinct from the karat (with a 'k'), which measures gold purity (24-karat = 100% gold). It relates to the gram (5 ct = 1 g) and the milligram (200 mg = 1 ct). Gem dealers commonly use 'points' for fractions (100 points = 1 carat).
- Diamond and gemstone retail and valuation
- Jewellery manufacturing and design
- International gem certification (GIA, IGI)
A 1-carat diamond weighs 200 mg and is typically 6.5 mm across. The Hope Diamond is 45.52 carats (9.1 g).
What is the Grain?
The grain equals exactly 64.79891 milligrams (0.06479891 g) and is the smallest unit in the traditional avoirdupois weight system. Originally based on the average mass of a single grain of wheat or barley, the unit was standardized to its current value with the 1959 international yard and pound agreement. The grain is still used in pharmaceutical compounding (some older drug formulations specify grains, especially aspirin and codeine), arrow tips and ammunition (bullet weights are commonly given in grains — a 9 mm bullet is around 115 grains), and precious-metal weighing (one troy ounce = 480 grains). It relates to the ounce (437.5 grains = 1 oz avoirdupois), the pound (7,000 grains = 1 lb), and the milligram (1 grain ≈ 64.8 mg). The unit reflects medieval agriculture's role in shaping early measurement systems.
- Bullet and gunpowder mass in ballistics
- Older pharmaceutical dosing in Anglo-Saxon countries
- Arrow shaft and archery equipment weights
A 9 mm bullet typically weighs 115–124 grains (7.45–8.03 g). Aspirin grain dosing: "5 grain aspirin" = 325 mg.