# Mcg to mg Calculator

Convert micrograms (mcg) to milligrams (mg) instantly. 1 mg = 1,000 mcg. Also shows grams, nanograms, and Vitamin D IU equivalents.

## What this calculates

Convert micrograms to milligrams by dividing by 1,000. This calculator also shows the equivalent in grams, nanograms, and Vitamin D International Units for supplement labels.

## Inputs

- **Micrograms** (mcg) — min 0 — Enter the amount in micrograms (mcg or µg).

## Outputs

- **Milligrams** (mg) — Weight in milligrams (1 mg = 1,000 mcg).
- **Grams** (g) — Weight in grams (1 g = 1,000,000 mcg).
- **IU (Vitamin D)** (IU) — International Units for Vitamin D (1 mcg = 40 IU).
- **Nanograms** (ng) — Weight in nanograms (1 mcg = 1,000 ng).

## Details

The microgram (mcg or µg) and milligram (mg) are both metric mass units, with 1,000 micrograms making up one milligram. Getting this conversion right matters for medications and supplements, where a 1,000-fold error can be dangerous.

**Formula:** mg = mcg / 1,000

**Metric Mass Scale:**

| Unit | Symbol | In Grams |
|------|--------|----------|
| Kilogram | kg | 1,000 g |
| Gram | g | 1 g |
| Milligram | mg | 0.001 g |
| Microgram | mcg (µg) | 0.000001 g |
| Nanogram | ng | 0.000000001 g |

**Common Supplement Conversions:**

| Supplement | Common Dose | In mg |
|-----------|-------------|-------|
| Vitamin D | 1,000 mcg (40,000 IU) | 1 mg |
| Vitamin B12 | 500 mcg | 0.5 mg |
| Folic acid | 400 mcg | 0.4 mg |
| Selenium | 200 mcg | 0.2 mg |
| Chromium | 200 mcg | 0.2 mg |
| Biotin | 5,000 mcg | 5 mg |

**Vitamin D note:** Vitamin D labels sometimes use IU (International Units) instead of mcg. The conversion is 1 mcg of Vitamin D = 40 IU. So 25 mcg = 1,000 IU, and 125 mcg = 5,000 IU.

## Frequently Asked Questions

**Q: How many mcg are in 1 mg?**

A: There are 1,000 micrograms (mcg) in 1 milligram (mg). To convert mcg to mg, divide by 1,000. To convert mg to mcg, multiply by 1,000.

**Q: How do I convert Vitamin D from mcg to IU?**

A: Multiply the mcg by 40. For example, 25 mcg of Vitamin D = 25 x 40 = 1,000 IU. This conversion factor (1 mcg = 40 IU) is specific to Vitamin D and does not apply to other vitamins.

**Q: Why do some labels use mcg and others use mg?**

A: Substances dosed in very small amounts (like B12, folic acid, and selenium) use micrograms because the numbers are more readable. Saying 400 mcg is clearer than 0.4 mg for consumers, even though they are the same amount.

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Source: https://vastcalc.com/calculators/conversion/mcg-to-mg
Category: Conversion
Last updated: 2026-04-08