A tinned food listing a low protein figure often contains more protein than a dry food listing a much higher one. The discrepancy is entirely about water.
Why percentages are not comparable
Every figure on a guaranteed analysis panel is a share of the food as it sits in the packet, water included.
Dry food typically contains a small fraction of water. Tinned food is mostly water, which means every other component is diluted by comparison.
Comparing the two directly compares two different things. The percentages are calculated against denominators that differ by a factor of several.
Removing water from the calculation
The correction is to express each nutrient as a share of what remains once water is taken out, which puts both products on the same footing.
The arithmetic is simple: subtract the moisture figure from one hundred to get the dry matter share, then divide the nutrient figure by that share.
Performing this on a tinned food usually produces a figure far higher than the label suggests, often reversing the apparent ranking against a dry product.
Where the comparison still fails
Dry matter basis corrects for water and nothing else. It does not touch digestibility, amino acid profile or ingredient quality.
Nor does it address energy density, which is what actually determines portion size. A food can be high in protein on a dry matter basis and still be fed in small amounts because it is calorie-dense.
The most useful single comparison remains nutrients per unit of energy, since a dog eats to meet its energy requirement rather than to reach a weight of food.
Why the confusion persists
Labels are required to state composition as fed, which is the honest description of what is in the packet.
The consequence is that the legally required presentation is the one least suited to comparison, and nothing on the packaging prompts the correction.
Marketing occasionally exploits this by presenting as-fed figures for one product against dry matter figures for another, which is why the moisture line is worth checking first.
What it means for mixed feeding
Owners who feed part wet and part dry are combining two foods with very different water content and energy density.
Substituting by volume or by eye rather than by calories is the usual route to gradual weight gain, because a small reduction in dry food rarely offsets the added wet portion.
Working from the calorie figure on each product, and treating the day as a single energy budget, avoids most of that drift without requiring any calculation about protein at all.