mg is mass, cc is volume — density connects them
Milligrams weigh a substance; cubic centimetres measure the space it fills. They only convert through density. For water, density is 1000 mg/cc, so 1000 mg = 1 cc and 1 mg = 0.001 cc. Mercury is 13,546 mg/cc, so the same 1 cc weighs 13,546 mg. One cubic centimetre equals one millilitre exactly.
Density of common substances
| Substance | Density (mg/cc) | 500 mg equals |
|---|---|---|
| Ethanol | 789 | 0.63 cc |
| Cooking oil | 916 | 0.55 cc |
| Water | 1000 | 0.50 cc |
| Milk | 1035 | 0.48 cc |
| Glycerin | 1261 | 0.40 cc |
| Corn syrup | 1380 | 0.36 cc |
| Honey | 1420 | 0.35 cc |
| Mercury | 13,546 | 0.037 cc |
Density in mg/cc is just density in g/ml times 1000, so a substance at 0.92 g/ml is 920 mg/cc.
Medication is a different mode
For a liquid medicine you divide the dose by the concentration on the label, not by a physical density. A 250 mg/5 cc suspension is 50 mg/cc, so a 200 mg dose is 4 cc. This is where errors turn dangerous: mixing up cc with mg, or using an infant strength where a child strength was meant, has caused overdoses. Read the concentration every time and check the strength.
Common questions
How many cc is 500 mg?
It depends on the substance. For water, 500 mg is 0.5 cc. For oil (about 916 mg/cc) it is roughly 0.55 cc, and for honey (about 1420 mg/cc) about 0.35 cc. You need the density before you can answer.
Is 1 cc the same as 1 ml?
Yes, exactly. A cubic centimetre and a millilitre are the same volume, used interchangeably in medicine and chemistry. The confusion to avoid is mixing up cc (volume) with mg (mass).
How do I convert a drug dose in mg to cc to give?
Divide the prescribed dose in mg by the medicine concentration in mg/cc printed on the label. A 200 mg dose of a 20 mg/cc syrup is 200 divided by 20, which is 10 cc. Always read the label; infant and child strengths differ.
