Micrograms to Milligrams Converter (mcg ↔ mg)

Convert between micrograms (mcg / µg) and milligrams (mg) in both directions. Common for medication dosing, vitamin labels, and lab values.

Last updated: September 2026

Compare 3 scenarios

Direction

Amount

Fill in the required fields to see your result.

Compare with similar

mg to mL Calculator (with Concentration) Ounces to Milliliters Converter (fl oz ↔ mL) Blood Pressure Risk Assessment Calculator Pediatric Fever Medication Calculator

About this calculator

The prefix "milli-" means one-thousandth and "micro-" means one-millionth. So 1 milligram (mg) = 1000 micrograms (mcg or µg). To convert mcg → mg, divide by 1000. To convert mg → mcg, multiply by 1000.

Medication packaging in the US commonly uses "mcg" instead of "µg" because the Greek µ character is hard to type and read on prescriptions — the FDA-recommended abbreviation for micrograms is "mcg" for exactly that reason. Wrong-unit errors are a top-10 medication-error category, especially with drugs where the therapeutic mcg dose is nearly the toxic mg dose (levothyroxine, digoxin, some benzodiazepines).

Helpful anchors: levothyroxine 100 mcg = 0.1 mg. Vitamin B12 1000 mcg = 1 mg. Digoxin 0.25 mg = 250 mcg. Always double-check the unit written on the label matches the intended prescription; when in doubt call the prescriber.

How to use

Example — mcg to mg. 500 mcg / 1000 = 0.5 mg. A typical folic acid tablet is 400 mcg = 0.4 mg. Example — mg to mcg. 0.075 mg × 1000 = 75 mcg. A common levothyroxine strength is 75 mcg = 0.075 mg. Switching between mg and mcg on medical labels is a leading source of tenfold dosing errors.

Frequently asked questions

What is the difference between mcg and µg?

None — they mean the same unit (microgram). "mcg" is the FDA-preferred plain-ASCII abbreviation because handwritten "µ" can be misread as "m" (giving a 1000× overdose). If you see "µg", "ug", or "mcg", they are equivalent.

Why does my prescription list 0.5 mg but the pill bottle says 500 mcg?

They are equal: 0.5 mg = 500 mcg. Different pharmacies use different unit conventions; the FDA does not mandate one. Always verify the strength on the label matches the prescribed dose numerically after unit conversion.

Are mcg and mg used for the same medications?

Different medications have very different therapeutic doses. Thyroid hormones, hormonal contraceptives, and some benzodiazepines are typically prescribed in mcg. Antibiotics, NSAIDs, and most oral chemotherapy are in mg. High-potency drugs use mcg; medium-potency drugs use mg.

Can I convert to grams (g) too?

Yes — 1 g = 1000 mg = 1 000 000 mcg. So 1500 mg = 1.5 g and 500 000 mcg = 0.5 g. Grams are used for high-dose IV medications (grams of ceftriaxone, for example) rather than oral tablets.