How Do You Convert Milligrams to Carats?
Divide milligrams by 200 to get carats. The formula is: Carats = Milligrams / 200 (or multiply by 0.005). The metric carat is defined as exactly 200 milligrams.
Tom Brewer weighs a gemstone fragment on a laboratory balance. The display reads 347 milligrams. Converting: 347 / 200 = 1.735 carats. He notes this would be reported as 1.73 carats on a gemological certificate because the convention is to round down to two decimal places.
Small Weight Reference
| Milligrams | Carats | Reference |
|---|---|---|
| 2 mg | 0.01 ct (1 point) | Tiniest commercial diamond |
| 10 mg | 0.05 ct | Small melee stone |
| 50 mg | 0.25 ct | Quarter carat |
| 100 mg | 0.5 ct | Half carat |
| 200 mg | 1.0 ct | One carat |
| 500 mg | 2.5 ct | Large solitaire |
| 1,000 mg | 5.0 ct | Museum quality |
| 5,000 mg | 25.0 ct | Exceptional rarity |
Practical Applications
Lab Analysis
Maya Singh identifies an unknown mineral sample in geology lab. She weighs it at 156 mg = 0.78 carats and measures dimensions of 5.2 x 4.1 x 3.0 mm. From these, she calculates density and compares to reference data. The weight in carats helps her estimate potential value if the stone turns out to be a precious gemstone (it ends up being a nice piece of zircon).
Jewelry Repair
Leah Novak brings a broken necklace to a jeweler. Three small stones fell out and need to be replaced. The jeweler weighs the originals: 42 mg, 38 mg, and 45 mg = 0.21, 0.19, and 0.225 carats. She orders replacement stones matching the closest standard sizes: 0.20, 0.20, and 0.22 carats. The total difference of 5 mg (0.025 carats) is invisible once set.
Historical Research
Priya Patel writes about historical jewels. A 17th-century inventory lists a diamond at "4 rattis" (an old Indian weight unit). One ratti = approximately 121.5 mg, so 4 rattis = 486 mg = 2.43 carats in modern terms. She converts historical weights to modern carats and milligrams so readers can understand the actual size of ancient gems.