What’s the Difference?
Gram (gm), milligrams (mg), and micrograms (mcg) are units of weight. To visually represent the relationship between the three units, think of a microgram as a miniscule grain of rice, a milligram as a small bite of rice, and a gram as the whole bowl of rice.
- 1 gm = 1,000 mg
- 1,000 mg = 1,000,000 mcg (µg is the short unit symbol for microgram)
International Unit (IU) is a unit of measurement but NOT a measure of weight. It’s the quantity of a specific biologically active substance that produces a particular biological effect. IU is most commonly used for medications, vaccines and some vitamins. However, converting an IU to a unit of weight isn’t a simple equation. That’s because an International Unit is based on the potency or concentration of the substance which varies from substance to substance.
Vitamin D: Converting Biological Activity to Weight
Vitamin D exists in a couple of different forms — cholecalciferol (vitamin D3) and ergocalciferol (vitamin D2). There are common vitamin mass equivalents for vitamin A, C, D, and E with each vitamin having a different biological equivalent. See Vitamin Conversion Chart. To get the equivalents of other substances, you would need to ask a pharmacist.