mcg to mg Converter
Micro means millionth and milli means thousandth, so 1,000 mcg = 1 mg exactly. Enter an amount, pick the direction, and the conversion — plus the gram equivalent — appears instantly.
Example: with Amount 1000 · Direction mcg to mg → Converted: 1 mg.
Computed by the calculator below using its default values. Change any input to see your own numbers.
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Check it outmcg vs mg: a factor of exactly 1,000
Both units are metric mass. A milligram is one thousandth of a gram; a microgram (mcg, also written µg) is one thousandth of a milligram. So mg = mcg ÷ 1,000 and mcg = mg × 1,000 — no rounding, ever. A 1,000 mcg vitamin B12 tablet is exactly 1 mg; a 400 mcg folic acid dose is 0.4 mg; 25 mcg of vitamin D is 0.025 mg (the same as 1,000 IU).
Labels print mcg instead of µg because a handwritten µ is easily misread as m — a 1,000× error. That’s also why mixing up the two units is dangerous: levothyroxine is dosed in micrograms (75 mcg = 0.075 mg), and reading that as milligrams would overstate the dose a thousandfold. When a label mixes units, convert everything to one unit first, then compare.
How it’s calculated
mg = mcg ÷ 1,000 and mcg = mg × 1,000 — exact by definition, since the SI prefixes make a milligram one thousandth of a gram and a microgram one millionth. The grams row divides milligrams by another 1,000. No density or substance information is needed, because both units measure mass.
Results update as you type and are estimates, not professional advice — verify important decisions with a qualified professional.
Common mistakes
- Reading mcg as mg — they differ by 1,000×, the most dangerous mix-up on medicine labels.
- Multiplying when you should divide: going from mcg to mg makes the number smaller.
- Confusing mcg with IU — international units measure biological activity and convert differently for each vitamin.
Frequently asked questions
How many mcg in a mg?
Exactly 1,000. The prefix micro- means one millionth of a gram and milli- means one thousandth, so 1 mg = 1,000 mcg by definition.
Is 1000 mcg the same as 1 mg?
Yes — 1,000 mcg equals exactly 1 mg. A 1,000 mcg B12 supplement and a 1 mg one are the same dose.
What is mcg vs mg on labels?
mcg (µg) is the smaller unit, used for potent nutrients like B12, folate, and vitamin D; mg is 1,000× larger. Labels prefer mcg over µg to avoid misreading.
How do I convert mg to mcg?
Multiply by 1,000: 0.4 mg = 400 mcg and 2.5 mg = 2,500 mcg. Equivalently, move the decimal point three places to the right.