Mass, volume and proportion
Milligrams express mass. Millilitres express volume. A percentage expresses a relationship per hundred units, but needs to specify which relationship. The international reference for unit names and symbols is the BIPM’s SI Brochure. Notation is not decoration: it prevents comparisons between different quantities. BIPM: International System of Units
A 10 ml bottle describes a volume, not the amount of a particular ingredient. A declaration of 1,000 mg needs to say whether it refers to the total amount of that ingredient in the container or another reference. A 10% figure requires knowing whether it is expressed as mass per mass, mass per volume or another defined basis.
A label calculation, not a recommendation
A purely illustrative example: a mixture contains 500 mg of a component in 10 g of product. Since 10 g equals 10,000 mg, the mass fraction is 500 divided by 10,000: 0.05, or 5% m/m. The calculation describes composition. It does not indicate an amount a person should use.
A second example: 500 mg of that component in a final volume of 10 ml corresponds to 50 mg/ml. This is a mass-per-volume concentration. Converting it into a mass percentage would require knowing the total mass of those 10 ml. Assuming every liquid has the same density as water introduces a condition that may be false.
The container total changes the reading
The same concentration can appear in containers of different sizes. If the formulation is homogeneous and the concentration well defined, a larger container can hold a greater total amount without being more concentrated. Conversely, a higher total figure does not itself demonstrate a higher proportion.
Imagine 20 mg/ml in a 10 ml container and the same concentration in a 30 ml container. The theoretical totals would be 200 and 600 mg respectively. The proportion per volume does not change. This mathematical example does not correspond to verified products or account for filling tolerances or uncertainty: it separates concentration from total amount.
Small units matter too
A gram contains a thousand milligrams; a milligram, a thousand micrograms. Losing a prefix introduces a factor of a thousand. Similarly, mg/g and mg/ml are not interchangeable without information on the relationship between mass and volume. Before comparing columns, check every symbol, including the less prominent ones.
The simplest way to review a label is to write a sentence: “this many milligrams of this substance per this amount of product”. If you cannot finish it, information is missing. Once it is clear, the arithmetic is usually straightforward. The aim is not to calculate consumption, but to prevent three ways of presenting numbers from creating a misleading comparison.
Take this with you
Before comparing a figure, complete its unit and denominator: total amount, concentration and volume are different pieces of information.
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