Convert Grains to Milligrams
1 grain (gr) equals 64.79891 milligrams (mg).
1 gr = 64.79891 mg
Type in either box. Scientific notation works: 1.5e-3.
Converting a list? Use the bulk grain to milligram converter to paste a column from Excel.
How to Convert Grain to Milligram
- 1 gr = 64.79891 mg
- 1 mg = 0.01543235835 gr
- Example: convert 15 gr to mg: 15 gr = 15 × 64.79891 mg = 971.98365 mg
Reference conditions. gr: Avoirdupois system: 1 lb = 16 oz = 7000 grains = 0.45359237 kg exactly (1959 agreement).
Formula
mg = gr × 64.79891
Derivation from SI units:
- 1 gr = 1/7000 lb = 64.79891 mg (exact)
- 1 mg = 10⁻⁶ kg = 10⁻³ g
- 1 gr = 0.00006479891 kg ÷ 0.000001 kg per mg = 64.79891 mg
Both units are defined exactly, so the factor is exact. Grain definition: grain; Milligram definition: milligram.
Worked examples
- An aspirin dose of 5 gr is 323.99455 mg.
5 gr × 64.79891 = 323.99455 mg - A 55 gr bullet is 3563.94005 mg.
55 gr × 64.79891 = 3563.94005 mg
Grain to Milligram conversion table
| Grains (gr) | Milligrams (mg) |
|---|---|
| 1 gr | 64.79891 mg |
| 5 gr | 323.99455 mg |
| 10 gr | 647.9891 mg |
| 15 gr | 971.98365 mg |
| 20 gr | 1295.9782 mg |
| 40 gr | 2591.9564 mg |
| 55 gr | 3563.94005 mg |
| 100 gr | 6479.891 mg |
| 115 gr | 7451.87465 mg |
| 124 gr | 8035.06484 mg |
| 150 gr | 9719.8365 mg |
| 180 gr | 11663.8038 mg |
| 300 gr | 19439.673 mg |
| 1000 gr | 64798.91 mg |
| 7000 gr | 453592.37 mg |
Where it's used
Grain weights from ammunition and older pharmacy texts are converted to milligrams or grams. 1 grain is exactly 64.79891 mg.
Grain to other weight and mass units
| Conversion | 1 gr equals |
|---|---|
| grain to kilogram | 0.00006479891 kg |
| grain to gram | 0.06479891 g |
| grain to milligram | 64.79891 mg |
| grain to microgram | 64798.91 µg |
| grain to metric ton | 6.479891 × 10⁻⁸ t |
| grain to pound | 0.0001428571429 lb |
| grain to ounce | 0.002285714286 oz |
| grain to stone | 0.00001020408163 st |
| grain to short ton | 7.142857143 × 10⁻⁸ ton (US) |
| grain to long ton | 6.37755102 × 10⁻⁸ ton (UK) |
| grain to troy ounce | 0.002083333333 oz t |
| grain to carat | 0.32399455 ct |
Frequently asked questions
How many mg is 1 grain?
Exactly 64.79891 mg.
How many milligrams are in 1 grain?
1 gr = 64.79891 mg.
How do I convert grains to milligrams?
Multiply the value in gr by 64.79891. For example, 15 gr × 64.79891 = 971.98365 mg.
Is the gr to mg conversion exact?
Yes. Both units are defined exactly, and 1 gr is exactly 64.79891 mg.
Sources
- Guide for the Use of the International System of Units (SI), NIST Special Publication 811, 2008 Edition, National Institute of Standards and Technology , Appendix B.8, "grain (gr)".
- The International System of Units (SI), 9th edition (SI Brochure), Bureau International des Poids et Mesures , Table 7, SI prefixes.
Last reviewed: . Factors are stored exactly and computed with 50-digit decimal arithmetic. See how we verify conversion factors.
Cite this page
APA
Scientific Converters. (2026, October 15). Convert Grains to Milligrams. Retrieved October 17, 2026, from https://scientificconverters.com/mass/grains-to-milligrams/
IEEE
Scientific Converters, "Convert Grains to Milligrams," scientificconverters.com. Accessed: Oct. 17, 2026. [Online]. Available: https://scientificconverters.com/mass/grains-to-milligrams/