How to convert mg to ml?

Question asked by Alice:

I would like to know how to convert mg to ml. Specifically, what is 15mg in liquid (IE: ml)?

Follow-up responses...

Milligrams (mg) and milliliters (ml)

posted by Robert:

Milligram (mg) is a unit of mass/weight and milliliter (ml) is a unit of liquid volume. The conversion cannot be done unless you supply some more information - a density or concentration. If you do supply some more information, its a matter of using proportion.

Answer to converting mg to ml

posted by mystic:

1 ml is 1/1000 of a liter, which is a volume. 1 mg is 1/1000 of a gram which is a weight. So, you cannot convert them easily. You need to know the concentration of the liquid to be able to achieve it.

If the liquid is water, it can be converted using the following information:

1 liter of pure water equals 1 kg (kilogram). So, if you are trying to convert a liquid similar to water, an approximation can be achieved with: 1ml = .001mg (1 ml is 1/1000 liter; 1 mg is 1/1000000 kg).

In this case, if the medicine in similar to water in weight, it would be approximately 100 mg=0.1ml.

Apples to oranges... the answer

posted by Chris:

The concept is actually pretty simple - to answer any of these questions you need one piece of additional information:

How many mg are there per ml of stuff you're measuring?

Every single drug ever made that is in liquid form MUST list the "concentration" of the liquid in question.... some drugs even have multiple forms with multiple concentrations. Much like not everyone likes a lot of sugar in their coffee, not all drugs have the same amount of drug per milliliter, cup, or whatever unit you're asking about. Each drug company makes their drugs in standard concentrations and these can be found on any container labeled appropriately for the particular drug in question - in fact, pharmacies that dispense meds are REQUIRED to have this info on the label.

Example - most diphenhydramine (Benadryl) liquid comes in a concentration of 12.5mg per teaspoon (1 tsp = 5ml). So if someone wants 50mg, they need 4 tsp or 20ml.
Editor's note: see the weight to volume calculator tool ( for help with your conversion.