What is a Milligram?

The milligram equals one thousandth of a gram (0.001 g) or 10⁻⁶ kilograms, and is the standard unit for pharmaceutical dosing, vitamin labeling, food additives, and chemistry laboratory work. A typical aspirin tablet contains 325–500 mg of active ingredient, and recommended daily vitamin C intake is around 75–90 mg. The milligram is essential in toxicology (LD50 values are often given in mg per kg of body weight), water-quality testing (dissolved minerals in mg/L), and trace-element analysis. It relates to the gram (1,000 mg = 1 g), the microgram (1,000 µg = 1 mg), and the grain (1 grain ≈ 64.8 mg). Pharmaceutical prescriptions worldwide rely on milligrams, and accurate sub-milligram balances are standard in research and pharmacy environments.

Visual reference for how the milligram relates to other weight units. Each row links to the full converter for that pair.

• Prescription and over-the-counter drug dosing
• Vitamin and mineral supplement labelling
• Trace element analysis in laboratories

• ✓1 mg = 1/1000 g = 1,000,000 µg. Always check which prefix the label uses.
• ✓Read medication labels carefully — confusing mg and µg can be a 1000× dosing error.
• ✓Nutrition labels list minerals in mg and vitamins (A, D, K) in µg.

• ✗Reading 500 mg as 500 g on a medicine bottle — a potentially fatal 1000× error.
• ✗Confusing mg (milligram) with mg/kg (dose per kilogram of body weight).
• ✗Mixing up mg and µg — µg is 1000× smaller.