What does mg stand for? In nearly every everyday case it stands for milligram, a metric unit of mass equal to one thousandth of a gram. It is the unit printed on pill bottles, vitamin labels and the nutrition facts panel for things like sodium and caffeine.
A milligram is very small. A thousand of them make one gram, and a paper clip weighs about a gram. That is why mg is the go to unit for medicine doses, where tiny amounts matter.
Quick facts
Stands for
MilligramSize
1 mg = 0.001 gram; 1,000 mg = 1 gramType
Metric unit symbolHow to write it
Lowercase mg, no period, no s for pluralUsed in
Medicine labels, supplements, nutrition facts, lab resultsOther meanings
Mg for magnesium, MG for Major GeneralNot to be confused with
mcg (microgram) and mL (milliliter)
The milligram abbreviation, broken down
The two letters come from the two parts of the word:
| Letter | Part of word | Meaning |
|---|---|---|
| m | milli | One thousandth |
| g | gram | The base metric unit of mass |
The same prefix shows up in millimeter (mm) and milliliter (mL). Because mg is an official metric symbol, it follows symbol rules: lowercase letters, no period and no added s. You write 5 mg, never 5 mgs. or 5 Mg.
Where the abbreviation for milligram shows up
- Medicine bottles: "Ibuprofen tablets, 200 mg" tells you how much active drug is in each tablet.
- Supplement labels: vitamin C or iron amounts per serving.
- Nutrition facts: sodium, cholesterol, calcium and potassium are listed in mg.
- Drinks: caffeine content on energy drinks and some coffee menus.
- Lab reports: results such as mg/dL, milligrams per deciliter of blood.
On a prescription label: "Take one 10 mg tablet by mouth once daily." Each pill holds ten milligrams of the drug, and you take one a day.
What does MG stand for in other fields?
Capital letters change the meaning, so look closely at how the letters are written.
| Form | Field | Meaning |
|---|---|---|
| mg | Measurement | Milligram |
| Mg | Chemistry | Magnesium, element 12 |
| MG | Military | Major General, a two star rank in the U.S. Army |
| MG | Weapons | Machine gun, on older maps and manuals |
| mg/kg | Medicine | Milligrams per kilogram of body weight |
A capital M with a small g, Mg, is the chemical symbol for magnesium. A label that says "Magnesium (Mg) 100 mg" uses both: the element and the amount.
mg vs mcg vs mL
These three are easy to mix up and the gap between them is large.
- mg, milligram: one thousandth of a gram.
- mcg or µg, microgram: one thousandth of a milligram. 1 mg = 1,000 mcg. See the page on mcg.
- mL, milliliter: a unit of volume, not mass. Liquid medicine is measured in mL, while the drug inside is listed in mg.
Reading mcg as mg would mean a dose a thousand times too large, so pharmacists take care to write units clearly. A liquid label often shows both: "160 mg per 5 mL."
How to say and write mg
Most people say the full word, "milligram," when they read mg aloud. In quick speech, nurses and pharmacists sometimes say "M G," but the full word is clearest.
- Leave a space after the number: 50 mg.
- Use lowercase letters, even when mg opens a table cell.
- Skip the period unless the unit ends a sentence.
- Do not add s: 1 mg, 250 mg.
For the larger unit, see the abbreviation for gram.
Mg stands for small amounts: some sizes to picture
- A typical low dose aspirin tablet in the United States is 81 mg.
- The daily value for sodium on U.S. food labels is 2,300 mg.
- One gram, about the weight of a paper clip, is 1,000 mg.
- One kilogram is 1,000,000 mg.
For more letters you see on labels and signs, browse the famous acronyms section.
Questions people ask
What does mg mean on a pill bottle?
It means milligrams, the amount of the active drug in each pill. A 500 mg tablet holds five hundred milligrams of that drug.
Is mg the same as mL?
No. Mg measures mass, how heavy something is. mL measures volume, the room a liquid fills.
How many mg are in a gram?
There are 1,000 milligrams in one gram.
Is it mg or mgs for plural?
Use mg for both one and many. Metric symbols never take an s, so write 20 mg, not 20 mgs.
What is the difference between mg and mcg?
A microgram (mcg) is one thousandth of a milligram. So 1 mg equals 1,000 mcg, and mixing them up can cause a serious dosing error.