Key points
- There is no fixed number of milligrams in a milliliter. A milligram (mg) measures mass and a milliliter (ml) measures volume, so one cannot be converted into the other on its own.
- The link between them is concentration, written as mg per ml (mg/ml). With it, mg = ml × concentration, and ml = mg ÷ concentration.
- One milliliter of water has a mass of about one gram (1,000mg), but that is the mass of the liquid, not of anything dissolved in it.
- UK law requires liquid foods to state their net quantity in units of volume, which is why a liquid supplement's size is given in ml.
How many mg are in a ml? It depends on the liquid. Milligrams measure mass and milliliters measure volume, so you need a third figure, the concentration, to move between them. A liquid labeled 20mg/ml has 20mg of the named substance in each milliliter. This guide explains the units, the arithmetic and why "1ml = 1,000mg" is usually the wrong answer.
Mass and volume are different measurements
The Weights and Measures Act 1985 defines both families of units. For mass, a gram is 1/1000 of a kilogram and a milligram is 1/1000 of a gram. For volume, a liter is a cubic decimeter and a milliliter is 1/1000 of a liter. The Act also defines a cubic centimeter as 1/1000 of a cubic decimeter, so one milliliter and one cubic centimeter are the same volume.
Mass tells you how much matter there is. Volume tells you how much space it takes up. Because they measure different things, no single number converts one unit into the other.
Labels use both. Regulation (EU) No 1169/2011, as it applies in Great Britain, says the net quantity of a food is expressed in units of volume (liters, centiliters or milliliters) for liquid products, and in units of mass (kilograms or grams) for other products. So the front of a liquid supplement gives its size in ml, while any figure for a named substance inside it is usually given in mg.
The link: concentration in mg/ml
Concentration is the mass of a named substance in a set volume of liquid. It is usually written as mg/ml or mg per ml, and sometimes per 5ml or another stated volume. BNF guidance on prescription writing asks for the strength of liquid preparations to be stated clearly, and gives "125 mg/5 mL" as its example.
Once you know the concentration, three simple formulas cover every conversion:
- mg = ml × concentration (mg/ml)
- ml = mg ÷ concentration (mg/ml)
- concentration (mg/ml) = total mg ÷ total ml
These formulas assume the substance is spread evenly through the liquid, and that the mg figure and the ml figure refer to the same thing.
Worked example 1: from a total to a concentration
An imaginary 50ml bottle contains 1,000mg of substance X in total. Its concentration is 1,000mg ÷ 50ml = 20mg/ml.
Worked example 2: how many mg in a measured volume
At 20mg/ml, 2.5ml of the same liquid holds 2.5 × 20 = 50mg of X.
Worked example 3: which volume holds a given mass
To find the volume that holds 50mg at 20mg/ml, divide: 50 ÷ 20 = 2.5ml.
These are round numbers for a made-up liquid, chosen to make the arithmetic easy to follow. They are not figures for any real product, and they are not amounts for anyone to take.
Why "1ml = 1,000mg" is usually wrong
The shortcut comes from water. The National Physical Laboratory (NPL) notes that at 4 °C a 10cm cube of water has a mass of a kilogram. A 10cm cube is one liter, so one milliliter of water has a mass of about one gram, or 1,000mg.
That shortcut fails in two ways. First, the NPL figure is for water, and a liquid with a different density has a different mass per milliliter. Second, and more important for labels, the 1,000mg is the mass of the whole milliliter of liquid. It says nothing about how much of a named substance is dissolved in it. A figure such as "20mg/ml of X" refers to X only.
Totals, concentrations and headline numbers
A liquid product can carry several kinds of figure, and they answer different questions:
| Label wording (illustrative) | What it measures |
|---|---|
| 50ml | The volume of liquid in the container (the net quantity) |
| 1,000mg of X per bottle | The total mass of X in the whole container |
| 20mg/ml | The concentration: the mass of X in each milliliter |
| 50mg per 2.5ml | The mass of X in a stated volume |
A total per container and an amount in a stated volume are different figures, even though both are in mg. Our guide What Does NRV Mean on a Supplement Label? covers the difference between a total per pack and an amount per portion, and Liposomal NAD+ and Other Formats, Explained covers how liquids, capsules and powders are measured differently.
Liquid medicines: ask a pharmacist
Many searches for "mg to ml" are about medicines. General arithmetic like the examples above is not the right tool for a medicine. The strength of a medicine is printed on its pack, and a pharmacist can check it with you, along with the measuring device that came with it. If anything on a medicine label is unclear, ask a pharmacist or your GP before using it.
If you came here to understand NAD+ rather than units, see the science page.
Pure Limitless sells one product: NAD+ Sublingual Drops, a food supplement.
Frequently asked questions
How many mg are in 1ml?
There is no single answer, because mg measure mass and ml measure volume. For a named substance in a liquid, the answer is the concentration printed as mg/ml. For plain water, one milliliter has a mass of about 1,000mg.
How do I convert mg to ml?
Divide the mass in mg by the concentration in mg/ml. At an illustrative 20mg/ml, 50mg is in 2.5ml. Without the concentration, the conversion cannot be done.
Is ml the same as mL?
Yes. BNF guidance notes that both "mL" and "ml" are recognized abbreviations for the milliliter; the capital L is a printing convention.
