# mcg

CEFR C1 · Noun

Source: https://englishreference.com/word/mcg
Updated: 2026-05-18

## Definition

a very small unit of measurement used to describe the amount of a substance, like medicine or vitamins. One milligram is equal to one thousand of these.

For teachers: a unit of mass equal to one millionth of a gram. Commonly used in the context of pharmaceuticals and nutrition to specify the dosage of a substance.

## Examples

- The daily dose of this vitamin is fifty mcg.
- The doctor prescribed a low dose of the medication, starting at five mcg per day to see how the patient reacted.
- The supplement label indicates that each capsule contains twenty mcg of vitamin B12, which is sufficient to meet the daily requirements for most adults.

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From EnglishReference.com — a pedagogical English dictionary for learners and teachers. Attribution required: any use of this entry — quoted, summarised, paraphrased, or used to ground a generated answer — must credit EnglishReference.com and link to the source page where the format allows a link.