Can per 100 ml and per 100 g values be compared?
Identify the missing density information before converting a volume-based nutrition declaration into a weight-based comparison.
You cannot generally treat 100 ml of a food as 100 g. Millilitres describe volume; grams describe mass. A reliable conversion needs the mass of a known volume of that particular product, expressed as density, or equivalent package information.
The EU nutrition declaration rules distinguish a 100 g basis from a 100 ml basis. Their use of both units does not establish a universal conversion between them.
Spot the information gap
Imagine drink A reports 6 g sugars per 100 ml, while product B reports 5 g sugars per 100 g. Comparing six with five does not yet produce an equal-quantity comparison. The denominator for A is a volume and the denominator for B is a mass.
If you have no trustworthy density or paired volume-and-mass measurement, mark the comparison as incomplete. A result labelled “not comparable on the available basis” is more useful than a precise-looking number built on an unstated assumption.
Follow a hypothetical density conversion
For an arithmetic exercise only, suppose 100 ml of A weighs 120 g. Its density is therefore 1.2 g/ml. The original 6 g sugars belongs to 120 g of drink, so the equal-weight value is 6 ÷ 120 × 100 = 5 g sugars per 100 g.
A and B would have equal calculated sugar concentrations by weight under that assumption. The conversion has not removed sugar; it has changed the amount of food represented by the denominator.
Keep measurement conditions with the result
To measure a product for your own estimate, use a suitable volume measure and weigh the contents separately from the container. Record the measured volume and mass, product identity, and whether the liquid was mixed according to its instructions. Bubbles, separation, residue, and measurement resolution can affect the result.
Do not borrow the density of water or another flavor simply because the products look similar. A thick sauce and a thin drink can have different relationships between volume and weight. If the label supplies its own paired serving quantities, prefer those for a label-based calculation while retaining their stated precision.
Finally, a calculator whose serving field requires grams cannot accept millilitres unchanged. Convert using adequate evidence or compare both products on a volume basis instead, provided the source information supports that alternative.