Micrograms to milligrams formula & decimal rule
In the SI metric system, a microgram is one-millionth of a gram or one-thousandth of a milligram. Therefore, 1 milligram equals 1,000 micrograms.
Milligrams = Micrograms ÷ 1,000 Example: 500 mcg ÷ 1,000 = 0.5 mg Fast 3-place decimal shift rule
To convert mcg to mg without a calculator, move the decimal point three places to the left:
- 5,000 mcg: 5000.0 → 5 mg
- 1,000 mcg: 1000.0 → 1 mg
- 500 mcg: 0500.0 → 0.5 mg
- 100 mcg: 0100.0 → 0.1 mg
Common vitamin & dietary supplement dosage chart
Over-the-counter supplements like Melatonin, Vitamin D3, and Vitamin B12 are frequently labeled interchangeably in micrograms or milligrams. Compare common retail supplement strengths:
| Micrograms (mcg / µg) | Milligrams (mg) | Common Supplement / Clinical Reference |
|---|---|---|
| 50 mcg | 0.05 mg | Vitamin D3 (2,000 IU daily dose baseline) |
| 100 mcg | 0.10 mg | Levothyroxine (Synthroid) thyroid dose / Vitamin K2 |
| 300 mcg | 0.30 mg | Low-dose Melatonin capsule |
| 500 mcg | 0.50 mg | Vitamin B12 sublingual tablet |
| 1,000 mcg | 1.00 mg | High-potency B12 / 1,000 mcg Melatonin |
| 3,000 mcg | 3.00 mg | Standard 3 mg Melatonin sleep-aid tablet |
| 5,000 mcg | 5.00 mg | Standard Biotin hair/skin dose / 5 mg Melatonin |
| 10,000 mcg | 10.00 mg | Maximum strength 10 mg Biotin or Melatonin |
Important clinical note: "mcg" vs. "µg" vs. "mg" safety
In medical prescription contexts, confusing milligrams and micrograms can result in a 1,000-fold dosing error.
- Symbol Standard: While µg is the official scientific symbol (using the Greek letter mu), medical guidelines (such as ISMP) strongly recommend writing mcg on drug labels to prevent confusion with "mg".
- Leading Zeros: Always write decimal milligram values under 1 mg with a leading zero (e.g., write 0.5 mg instead of .5 mg) to ensure safety.
Converting larger lab masses? Use our Milligrams to Grams Converter or Grams to Milligrams Converter.
Frequently asked questions
How many mg is 500 mcg?
500 micrograms (mcg) is equal to 0.5 milligrams (mg).
How many mcg are in 1 mg?
There are exactly 1,000 micrograms in 1 milligram.
Is 1,000 mcg the same as 1 mg?
Yes, 1,000 mcg is equal to exactly 1 mg.
Is mcg the same symbol as µg?
Yes. "mcg" and "µg" represent the exact same unit (microgram). "mcg" is preferred on healthcare labels to prevent misreading "µg" as "mg".