Dry Matter vs As-Fed: How to Convert and Compare, with a Worked Example
Dry Matter: Every nutrient percentage printed on a pet food label is expressed as-fed, water included (Regulation (EC) No 767/2009; AAFCO, 2024). Because a kibble holds 8 to 10% water and a wet food 75 to 80%, the same label figure means very different things across formats: water mechanically dilutes the wet food's numbers, making it look poorer than it is. Converting to a dry-matter basis removes the water and puts both foods on a common footing. The whole conversion rests on one formula: dry-matter rate = (printed rate divided by (100 minus moisture)) times 100. This guide works it through, step by step, with figures you can recompute yourself.
Last updated :General documentary information. For an individual animal, a veterinarian's advice takes precedence over any online content.
Why does moisture change how you read every percentage?
Answer capsule. Because every printed level is as-fed, water included. If 78% of a wet food's weight is water, only 22% of dry matter is left to carry all the nutrients, so each percentage is diluted (AAFCO, 2024). A kibble at 8 to 10% water and a wet food at 78% are not directly comparable. Removing the water by calculation restores a common basis.
Moisture governs the reading because the analytical constituents are declared on the product as it is, not on its dry fraction (Regulation (EC) No 767/2009). A kibble holds 8 to 10% water; a wet food 75 to 80%. The percentages of the wet food are therefore diluted by a mass of water the kibble simply does not contain, which distorts any as-fed comparison.
The effect can reverse a ranking entirely. A wet food declared at 10% protein can be richer than a kibble declared at 30% once the water is removed: 10% at 78% moisture works out to about 45.5% on a dry-matter basis, against 32.6% for the kibble (AAFCO, 2024). The unaware buyer concludes the opposite and systematically underrates the wet food. Conversion is what prevents that error, and it is the single most useful habit a label reader can build.
What is the conversion formula, step by step?
Answer capsule. Dry-matter rate = (printed rate divided by (100 minus moisture)) times 100. First work out the dry matter, 100 minus moisture; then divide the nutrient by it and multiply by 100. For a kibble at 8% moisture, dry matter is 92%, so 30% protein becomes (30 / 92) x 100, about 32.6% (AAFCO, 2024). The same formula serves protein, fat, fibre and ash.
The conversion takes one operation, applied in two steps. Step one: dry matter equals 100 minus the moisture percentage; for a kibble at 8% moisture that is 92%. Step two: divide the printed level by the dry matter and multiply by 100. A 30% protein level becomes (30 / 92) x 100, about 32.6% on a dry-matter basis, a value directly comparable with any other food converted the same way.
The final multiplication matters more than it looks. Dividing by the dry matter brings the level onto the water-free fraction; multiplying by 100 restores the percentage scale. Forgetting that last step divides the result by a hundred and breaks the comparison, a common error for anyone working from memory (AAFCO, 2024). The formula is identical for every constituent: a kibble at 8% moisture with 18% fat converts to (18 / 92) x 100, about 19.6%, and the same kibble with 3% crude fibre converts to (3 / 92) x 100, about 3.3%.
How do you compare two kibbles on a dry-matter basis?
Answer capsule. In three steps: find each food's dry matter (100 minus moisture), convert each nutrient with (rate divided by dry matter) times 100, then compare. Kibble A at 28% protein and 12% moisture gives (28 / 88) x 100, about 31.8%; Kibble B at 30% and 6% gives (30 / 94) x 100, about 31.9% (Tufts Petfoodology, 2021). The 2-point as-fed gap nearly vanishes.
Even between two dry foods, an as-fed comparison can mislead as soon as the moisture differs. A kibble's moisture commonly runs from 6 to 12%, enough to shift the printed levels (AAFCO, 2024). The worked case shows it: two kibbles that look two points apart on the bag, 28% against 30%, turn out nearly identical once converted, about 31.8% against 31.9%.
The reverse trap exists too. Two kibbles with the same as-fed level can diverge on a dry-matter basis if their moisture differs, so only conversion gives the real ranking (Tufts Petfoodology, 2021). When two kibbles share near-identical moisture, the as-fed reading is already close and conversion barely changes it; the gap becomes significant precisely when moisture diverges, something the label rarely highlights. Converting as a matter of habit avoids being caught either way. A simple worked check, dividing each protein figure by its own dry matter, takes seconds and turns a guess into a number you can defend.
How do you compare a kibble at 8% with a wet food at 80%?
Answer capsule. Convert each to a dry-matter basis first. The kibble at 8% moisture has 92% dry matter; the wet food at 80% has only 20%. A wet food at 12% protein gives (12 / 20) x 100, 60% on a dry-matter basis; a kibble at 30% gives (30 / 92) x 100, about 32.6% (AAFCO, 2024). The wet food comes out markedly higher despite an as-fed level far lower.
This is the extreme case where conversion is essential. The water gap reaches 72 points: the wet food holds only 20% dry matter to carry all its nutrients, against 92% for the kibble, so the as-fed reading has no nutritional meaning on its own (AAFCO, 2024). Applying the same formula to each, with its own moisture, is the only honest comparison.
The size of the swing surprises most buyers. On a wet food at 80% water, a 12% protein level multiplies by five on a dry-matter basis, because only a fifth of the weight carries the nutrients (Tufts Petfoodology, 2021). This water-leverage effect explains why so many wet-versus-dry comparisons end in reversed conclusions, and why intuition, which trusts the printed figure, is a poor guide across formats.
Is a wet food's fat level comparable with a kibble's?
Answer capsule. Not directly. A wet food's fat is diluted by 75 to 80% water, a kibble's by only 8 to 10%. A wet food at 6% fat and 78% moisture converts to (6 / 22) x 100, about 27.3% on a dry-matter basis, while a kibble at 15% and 9% converts to (15 / 91) x 100, about 16.5% (AAFCO, 2024). The wet food is, here, proportionally the fattier.
Comparing fat as-fed is misleading for the same reason as every other constituent: water cuts the printed level (Regulation (EC) No 767/2009). A wet food's 6% looks low while its real fat content, water aside, can be substantial. Only conversion exposes the truth, and here it flips the apparent ranking.
Fat is worth converting with particular care because it drives energy density and therefore the ration. Two foods identical on a dry-matter basis can still differ in kilocalories depending on their fat, so a full comparison pairs the dry-matter figure with energy density (NRC, 2006). Reading fat on a dry-matter basis avoids the quantity errors that follow from trusting the as-fed number.
What protein and fat levels should you aim for, read on this basis?
Answer capsule. Targets depend on species and life stage and are read on a dry-matter basis. A maintenance dog kibble often shows about 25 to 35% crude protein and 10 to 20% fat on a dry-matter basis; the obligate-carnivore cat needs a higher protein share (FEDIAF, 2021). These are indicative ranges, not maxima to exceed, and a vet adjusts them for an individual.
No single level suits every animal: the FEDIAF and AAFCO profiles set targets by species and stage (FEDIAF, 2021). A 30% protein level on a kibble at 8% moisture works out to about 32.6% on a dry-matter basis, which is the value you actually compare from product to product, not the as-fed figure on the bag.
Aim for a range rather than a ceiling, because "more" is not "better" beyond the need: excess fat mainly raises energy density and the risk of weight gain (WSAVA, 2021). A growing puppy or kitten needs more protein and energy than a neutered [spayed], low-activity adult, for whom an over-rich food drives weight gain. Tie the converted levels to energy density and body condition, and lean on veterinary advice where kidney disease, excess weight or growth is involved (NRC, 2006).
As-fed vs dry matter: the same foods, two readings
The table shows how the same printed figures change once converted, using the silo's worked examples. Each dry-matter value is recomputable with (rate divided by (100 minus moisture)) times 100.
| Food | Moisture | Printed level | Calculation | Dry-matter rate |
|---|---|---|---|---|
| Kibble | 8% | 30% protein | (30 / 92) x 100 | About 32.6% |
| Wet food | 78% | 10% protein | (10 / 22) x 100 | About 45.5% |
| Wet food | 80% | 12% protein | (12 / 20) x 100 | 60% |
| Kibble | 9% | 15% fat | (15 / 91) x 100 | About 16.5% |
| Wet food | 78% | 6% fat | (6 / 22) x 100 | About 27.3% |
The table is the whole argument in one view: the food that looks poorest on the bag is often the richest once water is removed. Read the right-hand column, never the printed one, when comparing across formats.
A clear method for converting and comparing
The recommendation is to make conversion automatic, not occasional. For any product you intend to compare, first read off the moisture and compute the dry matter as 100 minus moisture (AAFCO, 2024). Then convert each nutrient you care about with (rate divided by dry matter) times 100, remembering the final multiplication that restores the percentage scale. The same single formula handles protein, fat, fibre and ash alike.
Apply it without exception across formats, and as a precaution even between two kibbles. Between a kibble and a wet food the gap is dramatic and conversion is indispensable; between two kibbles it is smaller but still real once moisture diverges by a few points (Tufts Petfoodology, 2021). Converting both removes any doubt about which food is genuinely richer, and it costs nothing once the habit is formed. Treat the printed as-fed figure as a starting point and the converted figure as the one that decides.
Finally, remember what dry matter does not correct: energy density. Two foods identical on a dry-matter basis can differ in kilocalories depending on their fat, so pair the converted levels with the energy figure, requesting it from the maker if it is absent (NRC, 2006). Dry matter is the essential first step of a serious comparison, not the only one, and combining it with energy density and body condition is what turns a label reading into a sound feeding decision.
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Related questions: How do you convert a printed as-fed percentage to a dry-matter basis? | Why does moisture change how you read the printed percentages? | How do you compare two kibbles on a dry-matter basis?
Glossary: dry matter | moisture
Hub: Reading and decoding a label
Sources: Regulation (EC) No 767/2009 on the marketing and use of feed (EUR-Lex; retained in UK law); AAFCO, Understanding Pet Food (2024); FEDIAF Nutritional Guidelines (2021); WSAVA Global Nutrition Guidelines (2021); NRC, Nutrient Requirements of Dogs and Cats (2006); Tufts Petfoodology (2021).