Mcg to Mg Converter

A microgram (mcg) is one millionth of a gram. A milligram (mg) is one thousandth of a gram. That makes 1 mg equal to 1,000 mcg, so going from mcg to mg means moving the decimal point three places to the left¹.

What Mcg to Mg Conversion Measures

This tool changes the unit, not the amount. 400 mcg and 0.4 mg are the same quantity written two ways. It does not tell you how much of a nutrient anyone needs, and it does not judge a product.

The Formula

Metric prefixes are powers of ten. Milli means 10⁻³ and micro means 10⁻⁶, so the ratio between them is exactly 1,000 by definition¹.

Milligrams = micrograms / 1,000

Micrograms = milligrams x 1,000

How This Calculator Computes Your Result

Type the number printed on the label, in mcg. Decimals are allowed, for example 2.4. The tool divides by 1,000 by shifting the decimal point, so the answer is exact and is never rounded. Results appear in plain decimal form, never scientific notation, so 2.4 mcg shows as 0.0024 mg. The swap button opens the Mg to Mcg Converter with your result filled in, and the copy button copies the number.

What Your Result Means

The mg number is always 1,000 times smaller than the mcg number. This table converts the FDA Daily Values that appear in mcg on US labels, for adults and children aged 4 and older².

A quick sanity check: every value in this table is under 1 mg. If a label amount below 1,000 mcg gives an answer above 1 mg, the decimal moved the wrong way. On the same label, vitamin C (90 mg) and vitamin E (15 mg) are already in mg², so convert before comparing.

The adult recommended intake of vitamin B12 is also 2.4 mcg, or 0.0024 mg³.

Mcg to Mg Conversion Table

Why Labels Say "mcg" and Not "µg"

The official SI symbol for micro is the Greek letter µ¹. FDA label rules write "mcg" instead⁴. Health groups prefer it for safety. The Institute for Safe Medication Practices (ISMP) lists "µg" as an error-prone abbreviation because it can be mistaken for "mg", and advises "mcg"⁵. Mixing the two up is a 1,000-fold error.

ISMP flags two related slips. A trailing zero (1.0 mg) can be read as 10 mg, and a missing leading zero (.5 mg) can be read as 5 mg⁵. This converter always shows a leading zero (0.0024, not .0024) and drops trailing zeros.

Why IU Cannot Be Converted With One Factor

Some older labels use international units (IU). An IU measures biological effect, not weight, so the mg value of 1 IU depends on the substance. The NIH Office of Dietary Supplements gives these conversions:

• Vitamin D: 1 mcg equals 40 IU, so 20 mcg is 800 IU⁶.

• Vitamin E: 1 IU of the natural form equals 0.67 mg, and 1 IU of the synthetic form equals 0.45 mg⁷.

• Vitamin A: 1 IU of retinol equals 0.3 mcg RAE, and 1 IU of dietary beta-carotene equals 0.05 mcg RAE⁸.

For this reason the tool converts only mcg and mg. Current FDA rules require vitamin D in mcg, with IU optional in parentheses⁴, and vitamin E is now listed in mg⁷.

DFE and RAE Are Not Plain Weights

Folate is listed as "mcg DFE" (dietary folate equivalents). One mcg DFE equals 1 mcg of natural folate or 0.6 mcg of folic acid⁴. So 400 mcg DFE does not mean 400 mcg of folic acid in the tablet. This tool changes the unit only, hence 0.4 mg DFE.